Title: Building an engine tutorial
Sumer - May 24, 2007 08:19 AM (GMT)
The Quick Guide to designing a realistic and capable engine.
I thought it might be worth writing a quick guide to designing a piston engine for those of you out there who might be interested. All too often people will just assume they can add another thousand horsepower to a tank and be done with it, but it's not that simple. This guide will hopefully show you how complex an engine is, and at the same time guide you in designing the simple statistics to your own. My credentials, for those of you who may be curious, is a family history of maritime diesel use, my father, several uncles, and many many people I grew up around being marine diesel mechanics. I've had the luxury of hands on experience with these, especially high output, engines for many years now. I hope to pass this experience to you through this guide, at least as much as possible.
Step One: What do I want my engine to do?
This is probably the single most ignored step in all of NS for a piston engine. Piston engines, especially diesel, are temperamental and need to be custom tailored to specific tasks. Thankfully custom tailoring is rather easy, and a well designed base engine can be adapted to a wide variety of applications. But it is important to consider what use you will have for the engine in question, as they will all have issues. A marine diesel for a fishing boat will be different from one for a frigate because the fishing boat will need constant low speed power for days if not weeks of non stop running and little maintenance, a frigate on the other hand will often need speed while having the ability to stop the engine for extensive maintenance. Automotive gasoline engines will need to be small and lightweight, and need to use the commonly available fuel stocks, while still being reliable, which will cause them to suffer in terms of power. I will be concentrating on an engine for a tank for this example however, because this is where you are most likely to see the need for a piston engine on NS, and where most people are likely to mess up.
Now that we have decided what we want the engine to do, we know what we have to work with, or can figure out what we have to work with, in terms of space, power, speed, reliability, and fuel consumption. The engine for this example will be a fairly conventional engine to replace the MTU 870 series engine in a Leopard 2.
Step Two: How will my engine work?
This is probably the most crucial step because it will dictate everything. The first thing we need to consider is how the engine will cycle. What this means is we need to decide if this will be a two-stroke, four-stroke, or one of the more exotic designs like a six-stroke. They all have their advantages and disadvantages, all will greatly impact how the engine can operate. Some important thing to consider first is power stroke. The number of power strokes per cycle, in plain and simple English, is how many times the engine goes boom per times the piston goes up and down. Every stroke is approximately half a rotation of the crank shaft, meaning one stroke is the piston either moving up, or moving down. Now that you know what that is, we can move on to describe the different cycles.
The four-stroke cycle, also known as the Otto Cycle, is the standard cycle for most engines, especially in cars, airplanes, and tanks. The four stroke is a little less powerful then others, but makes up for it in much less fuel use. For most normal sized engines this is probably the best conventional approach to use. The four-stroke is a ¼ power stroke engine, meaning one out of every four strokes is a power stroke, the remaining three are used to draw in the fuel-air mixture, compress it, and eject it from the cylinder. This is good because it allows a more efficient combustion, and thus less fuel escaping unburned in the exhaust. The down side however is that the engine has to rotate two times for every power stroke, forcing the use of multiple cylinders for balance, and reducing power per RPM, or rotations per minute of the crank shaft. Four stroke engines typically have to run at a higher RPM to get sufficient power.
The two-stroke cycle is more commonly used on very large diesel engines, such as oil tankers, or very small engines such as model aircraft engines or lawnmower engines. The basic principal of the two-stroke is simple, the first stroke starts with the combustion of the fuel-air mix, forcing the piston to move down, which opens intake and exhaust ports on the cylinder walls and allows fuel-air mixture into the cylinder and exhaust out, while the second stroke compresses the fuel-air mixture and combustsit. This operation is very simple mechanically, and thus very easy to build small or large, but it has some serious problems. The need to use intake ports in the cylinder wall and one stroke for both intake and exhaust means that fuel will always end up unburned in the exhaust, and exhaust will always remain in the cylinder. This is bad because it means less efficient burn of the fuel-air mixture and very messy exhaust. The bonus of the two-stroke system is that it is a ½ power stroke engine, meaning that it has twice the power strokes per full rotation of the crankshaft as a four-stroke engine. Most two-stroke engines also operate with the fuel actually being a fuel-oil mixture, forcing the fuel air mixture into the cylinder below the piston during the compression stroke so that it lubricates the crankshaft and piston components before being combusted, which saves a lot of weight in oil systems but means that because of the added lubricating oil in the fuel, that combustion efficiency is even worse then normal. The bonus of using this, besides lubrication, is that the motion of the piston going down can be used to force the fuel-air mixture into the combustion chamber above the piston with more pressure, which better forces the exhaust out of the cylinder. Some tanks use this system, including the 5TD and 6TD engines in the T-64 and T-84 series tanks. They're usually very lightweight, powerful, and small, but more costly on fuel then a four stroke and generally very dirty.
Now earlier I mentioned the exotic six-stroke, so I will elaborate on it only briefly. There are several six-stroke engine systems out there, many working differently from each other. The basic idea however is the inclusion of two more strokes to the cycle to change a four stroke engine to a 2/6 power stroke, or 1/3 if you wish, instead of the ¼ power stroke of a four-stroke engine. I would generally recommend that you avoid these systems unless you know and understand the rest of the process first. After a little playing around with two and four stroke engines however, you may be interested to take a look, probably the most useful of the six-stroke engines however is the Crower cycle, because it is the easiest and most powerful. The others all have their places however, and might be worth some fun later on.
For our example engine we will be using the four-stroke system. We want range, decent power, and commonality with the vast majority of other systems around, as well we want to be a little environmentally friendly.
Step Three: Ignition, how will the fuel burn?
This may seem like a simple question to answer, but in fact it's not quite as simple as it may look. How the fuel is ignited in the engine will dictate what fuels the engine can actually run. We have two basic ways to take this, compression ignition and spark ignition. These are two differing camps in how to run an engine because they are essentially mutually exclusive. Gasoline and other similar fuels such as most jet fuels, require such a high pressure to com bust through compression that it is impractical to design an engine to use this system if gasoline is to be used. On the flip side, gasoline combustion under compression is significantly more efficient and powerful, but as stated, it will put exponentially more stress on the cylinder and piston, which means the engine will be significantly more likely to fail catastrophically. Diesel, however, is much much easier to burn under pressure, but doesn't flash light very well when sparked. So diesel engines will use compression, not have a spark plug, but instead they will have the force of the piston compressing the fuel-air mixture to burn. Gasoline engines will need to be sparked by an electrical ignition, a spark plug, to be used however. As we want a multifuel, and as we won't be running too high compression ratios in this engine, we will opt for compression and instead bulk up the engine to compensate for when we need to use gasoline. This means the engine will be heavier, quite a bit heavier, but it will allow us to fuel up on any commonly used engine fuel.
Step Four: Layout and displacement?
This is both one of the most important and most useless steps of them all. The easiest part to tackle is layout. Do you want an inline, a vee, a boxer? Maybe something more exotic like a W-engine or H or even an X layout. They are all essentially the same in terms to how it will effect the engine workings. Of the above the only thing really effected is the physical size of the engine. An inline engine will be long and narrow because each piston will be in a line. A vee engine will offset the pistons such that it is wider but shorter, and a W engine will take this even further to make a wide but short engine, but will limit the displacement of individual cylinders, and an H or X engine will be tall, wide, and short, but complicate externals such as fuel and intake/outlet systems. The vee engine is most common because it is the easiest to produce and maintain in the smallest package, and we will be using a vee engine for this. However, the other options we have, that I will discuss breifly here, are the boxer and one I didn't mention, the opposed piston. The boxer engine is essentially a vee engine but flat, so that cylinders are opposite of eachother. This removes the need for counterweights on the crankshaft of the engine and allows it to run smoother because the pistons balance eachother. This can increase power, but it does have the issue of being very wide. An opposed piston engine is entirely different all together. In an opposed piston engine you have two pistons, with two seperate crank shafts, sharing a single cylinder. This as many upsides, not the least of which being the ability to run higher compression ratios because the combustion pushes on two pistons instead of a piston and a head attached with a few bolts, allowing more pressure for less failure. Opposed piston engines can also get more power per cylinder of a given dimension because smaller cylinders still mean more movement of the pistons, allowing much more power from less displacement, which I will touch shortly. The major downside to the opposed piston engine however is increased complexity. The need for two crankshafts on opposite sides of the engine means you need to join them through a centrak gearing system before putting into a transmission, and of course it doubles the mechanics internally around them, for this reason they are often two-stroke engines.
Displacement is the single most important factor to how much power you can produce then anything else. American hot rodders have a saying that goes “no replacement for displacement” and this holds true everywhere. In short displacement is the internal volume of all the pistons combined at their maximum capacity. This is really just a combination of bore and stroke, which is how wide a diameter the cylinder is, and how long it is with the piston at the bottem of it's cycle. More displacement means more air, means more power from each deatonation, and means less wear on the engine because for a larger bore you need thicker cylinder walls. You can alternativly go with longer strokes and narrow bore, but this will actually suck power from the engine as the fuel will burn so quickly as to only act a certain ammount. Higher power engines typically are short stroke but wide bore diameter engines to increase power but decrease time between power strokes. Displacement is the hardest thing to change in an engine because it will require a complete redesign if it's more then a small percentage of the engine. So, rather then take you through all the details of how to make it, I will just wave my hand and decide we will be using a 48L displacement engine. This is a good average size, the MTU 870 series engine of the Leopard 2 for instance is 40L displacement, and will give us some nice power gain without seriously increasing the size of the engine. Another aspect of this that I will touch before we move on is number of pistons, because it is related to displacement. But first, MORE PISTONS DOES NOT MEAN MORE POWER. Repeat that to yourself several times until you have it memorized. More pistons means a lot of things, better balance, smoother exhaust and intake, more power strokes per rotationof the crank shaft. What needs to be considered most is that the displacement of the engine is the sum of the displacement of the individual cylinders, and thus to a point more cylinders allows you to make them smaller for more displacement. Ferrari uses this quite effectivly for instance, with the 4.7L V12 engine of the Ferrari F50 having about 0.4L per cylinder, so each cylinder is small, moves much shorter distances, and can be cycled quickly. For our engine we will have ten sylinders because it's a good number to keep the engine ballanced and vibration free, while at the same time allowing slightly larger cylinders for easier combustion of lesser fuels. But in reality we could go with a V10 or V8, or anything, it doesn't matter as long as the displacement is enough. So for now we have a 48L V10 engine running primarily on diesel fuel, but with multifuel capability.
Step Five: Inductuion and exhaust?
Now we are going to start to get fancy, but also complicated. So for ease I am going to address this in order, induction, exhaust, and then “other” for a few specialty things to add in.
Induction is simply how the air from outside the engine gets inside the engine to be burned. It is important to know that more air means more power, when you press the gas pedal to your car you're not really putting more fuel in the engine you're putting more air into the engine. So this is the part where you can get the most power. Here you have really two primary options, natural and forced induction. Natural induction means your engine will suck the air in itself and require no assistance, this is less powerful unless the engine is very carefully designed and maintained, but has the upside of being signifigantly less maintenance intensive. The other choice is forced induction, which means in short that air is forced into the engine by a compressor. Two basic types of this are the supercharger and the turbocharger. Now without going into all the different sub types of each I will just tell a basic outline of them. A turbocharger uses a turbine in the exhaust to turn a compressor that forces air into the engine. This takes no power from the engine itself, and can give a lot of air to the engine, but it has problems. The need to use exhaust means that you need to have high pressure exhaust right out of the engine to run the turbine, as well because of the excess ammount of air forced in turbocharger engines have to run at a lower compression ratio then naturally inducted engines. A final problem is what is known as turbo lag. This is means that the turbocharger does not deliver at lower RPM or initially, the engine must be kept running fast to keep enough exhaust pressure to run the turbine, and so a turbo is useless at lower speeds. Because generally the larger the turbocharger compressor, the larger the power boost, this inversely means that the larger turbocharger will take even more exhaust pressure to provide any boost. There are ways around this, such as using two or more smaller turbochargers that spool up quicker but provide slightly less power, which is the most common way of doing this. Another, not as common, approach is the use of a smaller turbocharger combined with a big one, so that the smaller unit will provide limited boost at lower RPM and allow the bigger one to spool up quicker, this helps but isn't seen as often because of the steep power curve it causes. Another alternative is the use of the turbocharger along with a supercharger, which gives the best of both worlds, provides a flatter power curve, but has some serious problems. At least one production car and race car has used this system before, but it is otherwise rare unless aftermarket installed. Although it is quite a bit more common on marine diesel engines.
The other forced induction option is what is known as the supercharger. It's essentially the same as a turbocharger except that instead of using a turbinr driven by exhaust gasses to run it is driven directly off of the engine itself. This has the downside of sucking a small ammount of power from the engine, but the upside is that at lower RPM speeds it provides substantial boost. Once RPM speeds get higher though the supercharger begins to suck more power then it provides, or even begin to suck air from the engine itself, and as such needs to be considered differently.
For exhaust the only think you need to really think about is if you're going to have a turbocharger. A turbocharger needs the exhaust to be run through the turbocharger turbine, and that means it may need to be routed oddly, causing an unnessecarily long exhaust system. Other then that, as long as the exhaust can freely move out of the engine and out of the exhaust system, then you are set.
The last part I will mention, as “others” here, are some things to include on this track. Air coolers, for instance, which cool the air down at various stages of the intake process. Cooler air is denser air, and thus more of it can be packed into a cylinder for more power. The most common cooler would be the intercooler, where air from the forced induction system is cooled before being put into the engine. Forced induction has the odd habit of heating the air it compresses, making it less dense at the same time, so an intercooler will change that to increase power.
Another thing to consider is fuel additives. Specifically water-methanol, propane, and nitrous oxide. They all have their uses and advantages, as well as disadvantages, but shouldn't be considered for industrial engines. I'll touch them breifly here because I know someone will try to install “NOS” on their tank engine at some point, and this will help teach you why that is a bad idea. N2O, nitrous oxide (Never “NOS”, that's a brand name of a company that produces kits for aftermarket add on to cars) is a system where quite simply N2O is injected into the engine. This syetem won't work with diesel engines, it will only work with gasoline and to a limited extent pure ethanol. N2O works two fold. First it drops the air temperature of the intake where it injected, meaning again denser air, and second durring combustion it breaks down and delivers more oxygen to the combustion process, which again adds more power. Because of the pressures involved though, this doesn't work with the relativly low pressure diesel combustion.
Water methanol works in a simmilar way, but is ideal with forced induction engines. What it is is essentially a combination of water and methanol, and is sprayed into the turbo or supercharger to prevent air from lighting under high boost compression in these systems. This means more boost, more air, more power.
Finally is propane injection, which is the counterpart to N2O in that it is the diesel counterpart. Injecting propane into a diesel engine will cause a more efficient burn still of the diesel combustion, and will give a little more power, and unlike the other two systems can be used constantly, but for much less power increase.
For all of this talk we will take our 48L V10 and add an intercooled twin turbosystem, with the option for propane injection to be used later if we need. This will give us a highly efficient engine with good reliabiity and power for a decent size. Now for statting it out.
Step Six: Good, now how much power do I have?
Now we get to the fun part. After we've understood all the parts going into the engine, and have a basic layout we can work with, we can begin making our stats. This is more guesswork then real math though, as every engine is different. But here I will give you the basic figures to know things that might be inportant to you. First we will cover power, the one everyone wants to know. To know power we must know the optimum RPM for the engine, for our example this will be a nice round 3000 RPM. Gasoline engines will need higher RPM to get more power, but diesel engines will typically opperate best in the lower speeds, with huge two-stroke engines of ships sometimes running as low as 94 RPM. But for us 3000 RPM will give us a good balance to run anything we need to while still getting power from our four-stroke system. A general rule of thumb here, appart from looking at real engines, is that the higher the displacement the lower the RPM, and this holds true for both gasoline and diesel engines. Lower RPM also means less wear and tear, and thus less maintenence. But how do we get power from this? This is where handwavey comes in. Power is a combination of more intracate things in the engine then I can detail to you in this guide, but a basic rule of thum to estimate it for diesel engines in the same application and setup as what we have is that you can get 20-35 horsepower per liter normally, 40-60 horsepower per liter with a turbocharged or supercharged engine, this is for these medium sized ones. And it is important to remember that the more power systems will need signifigantly more complex, heavier, and larger systems to get that power. These ratios are generally the best way to approach how to determine power. But remember that as engine speed increases the engine will make less power on the same ammount of displacement, but as engine size decreases it will make more power for the displacement, but this will rise less then the power will drop with speed. Smaller faster engines will need more complex systems, especially forced induction, to increase power, but will be able to do it much easier then larger engines because less volume needs to be compressed before being forced into the cylinder. Conversely lower speed engines will be less capable of producing the same ammount of forced induction boost pressures as faster engines, and larger ones will have more space to fill and thus need more intake and boost.
So, for our engine we have decided most of the important specifications, and now can work out the power. We'll go with a rounded number within the bracket we can have to make it easy, so we'll arbitrarily choose 2000 hp. It is important to remember this is engine power under ideal situations, and that hotter or cooler air outside will cause this to go down or up, as will altitude, and any number of factors. But as a good baseline we will go with 2000, which is realistic. Since we opted earlier, for fun, to install propane injection if we want, that can go up to 2100 with propane injection, but no higher.
So what about dimensions and weight? Well, engines are typically built out of steel and thus weight a lot and are big. You have two ways to go about doing this, first you can take the bore diameters you may have decided on earlier and add them up. If we have a bore diameter of 170mm then each cylinder plus walls, plus cooling and other systems will take uo about 200mm of diameter. So six of them, the length of a vee engine, will be about 1.2m. But then the additional parts on the front will add another 20-30cm, so the total length of the engine will be about 1.5m for easy rounding. These numbers can be played with to an extent, so it should be taken more as a guideline then anything, althougn don't go too radically different from them. And remember, reducing the ammount of surrounding space on the cylinder increases maintenance needs because there is less room for wear to happen before the cylinder fails completely. Width is a little more complicated, and depends on some weird math knowing the angle of the piston rods in the vee engine, and the stroke length. For inline engines this is just the width of the previous bore ammount, 200mm, plus about 20-30cm of additional stuff to the sides. So that an inline may be 40cm wide. A boxer is easy because it is just the stroke length plus 30-40cm. A vee however to get accurate you need to know the angle of the vee, which we will be lazy and say is 45 degrees. This way we can basically say if our stroke is say 200mm long, then our width from the centre will be 100mm, and so the total stroke length will be 200mm, plus 50-80cm of additional externals. Height will be done in a simmilar way to width, keeping in mind the height of a boxer is the width of an inline, and the height of an inline is half the width of a boxer. Vee engines are typically square in their sizes of height and width, or sometimes taller or sometimes wider, depending on stroke length. We have a short stroke length though so we'll do with a shorter engine height. Final rounded statistics then will be 1m wide by 1.5m long by 0.8m tall. This will give us a nice compact engine that is very capable. The other way to do this would have been to find an engine of simmilar displacement, layout, induction and speed, and copied their stats rounded as needed.
And then we need to do weight, which is much easier to do now because I will provide you with some numbers. First you can simply copy the weight of a simmilar sized and shape and laypout engine, or you can follow this. An average excellent power to weight ratio for the most modern engines is between 80 and 90 kg per liter of displacement. Going higher will cause serious problems, and older engines will be much lower. So our engine will thus weigh about 4000kg now.
The final performance aspect to consider is torque. It's not as important in NS because no one thinks of it, but it's worth a glance. Torque is a factor of engine speed and power, meaning the slower engines will produce more torque and the faster less. All I can really tell you without taking you through some nasty math is to keep the torque number around the power. So our 2000 hp engine will have abour 2200 lb-ft of torque, with roughly the same when propane injected to keep things simple. Now the final part.
Step Seven: The stats, yay!
This is the shortest, last, and best part. We're going to write our stats down, and we'll do it in a simple way. The simple stats we need are just this:
Configuration: V12 Twin Turbocharged
Power: 2000 bhp
Torque: 2200 lb-ft
We can however expand this if needed, or include this information in write ups for fun. An expanded list will look more like this.
Confugiration: 45 degree V12
Induction:Forced, twin turbocharged
Optimum RPM: 3000
Power: 2000 hp
Torque: 2200 ft-lb
Now there are all kinds of things we can discuss further such as fuel consumption, cooling systems, and other things. But they're not important to our needs, all that needs to be remembered is that these things exist. Bigger engines eat more fuel, more powerful engines and faster engines need more cooling capability. But for the short of it all, this is everything needed to design and implement an engine in detail or in simplicity in a design. And it may help you better understand how your own car works.
If there's anything I missed or that you want to have elaborated on, feel free to ask.
Appendix A: What not to do when building your engine
Ok, this is a breif add on that I have decided to add because I see these things happening all too often.
Don't assume all engines are equal.
This is straight forward, unless the engines you are looking at are doing virtually the same thing as what you need, then don't bother using them as a reference. A racing engine and a tank engine are completely different, and the characteristics of one will not carry over to the other's application. Especially with the case of racing engines which are fine tuned for a specific and very short service life. In theory you can stick a 1000 bhp racing engine in a tank, but it will last you all of an hour before it destroys itself. This is bad, very bad. Decide your application, find engines to assist you looking over from that application, and work from there. Don't mix-n-match, it simple doesn't work that way.
Don't turbocharge a Crower cycle.
For the same reasons it's a stupid idea to turbocharge a steam engine, you can't turbocharge a Crower cycle engine. Turbochargers need hot high pressure exhaust gasses to work, the whole injection of water into the cylinders completely ruins this and means your turbos actually reduce horsepower by restricting exhaust flow and intake flow, and add weight to the overall engine. Not to mention the water itself is not good for the turbine.
Don't add 1000 bhp to an existing engine.
Don't, simply don't. Most modern engines for use on anything but giant marine applications are so finely tuned to get the power they have now that you are virtually maxing out their potential power. You can not take the engine out of a Leopard 2 and add another thousand horsepower, you can't. You can't even take it and add five hundred horsepower without serious consequences. Yes the engine is rated at a maximum output of 1800 bhp, but running an engine at maximum rated output means you are running it into the ground and will have to replace it very very often.
Don't assume you can make an engine drmatically more fuel effecient.
Because you can't. An engine will run with X ammount of fuel injected per cylinder per cycle every time. That simply does not change. More or less air is added to create more burn and thus more or less power and speed inside the engine, but the fuel remains the same. And that ammount of fuel is decided by the displacement of the cylinders. The larger the cylinders, the more fuel injected. Thus the more power the more fuel used. The faster the RPM, the more fuel used. The fewer the number of cylinders per a set displacement, the more fuel used.
Don't mix engine types.
I've already explained the different engine layouts, but I want to make this clear anyway. You can't apply the same type of charactaristics to a V or H or I engine that you would to any other engine. Modifications made to an Opposed Piston engine, or even the general characteristics of it, do not apply to a Boxer engine. If you need to understand this please re-read the section above regarding that subject. But remember, they can't simple be changed from a B12 to an I12, or an Opposed 6 to a V6. Especially not with the likes of the Opposed Piston engines and other special ones like rotarys, radials, and other non-conventionals.
Appendix B: Real Life fuel/range ratios for modern tanks.
The below ratios are divided up into weight classes based on combat weight, and are taken only for MBTs which have a power/weight ratio at or above 20hp/tonne. Provided data comes from Janes Tank Recognition Guide, and includes stated range (Where nessecary the lower of two estimates is taken), fuel capacity, and from them their ratio.
50 tonnes or above:
- LeClerc (550km/1300L): 2.36L/km
- Leopard 2 (550km/1200L): 2.18L/km
- Arjun (450km/1610L): 3.58L/km
- Type 90 (400km/1100L): 2.75L/km
- Khalid (400km/950L): 2.38L/km
- M1A2 Abrams (426km/1907L): 4.48L/km
- Degman (700km/1450L): 2.07L/km
- T-80B (450km/1100L): 2.44L/km
- T-90 (550km/1200L): 2.18L/km
- M-84 (700km/1450L): 2.07L/km
- T-84 (540km/1300L): 2.4L/km
- AMX-30 (500km/970L): 1.94L/km
30 tonnes or less:
- TAM (940km/640L): 0.68L/km
ChevyRocks - May 24, 2007 04:11 PM (GMT)
Well, one thing I see...
|I'll touch them breifly here because I know someone will try to install “NOS” on their tank engine at some point, and this will help teach you why that is a bad idea. N2O, nitrous oxide (Never “NOS”, that's a brand name of a company that produces kits for aftermarket add on to cars) is a system where quite simply N2O is injected into the engine. This syetem won't work with diesel engines, it will only work with gasoline and to a limited extent pure ethanol. N2O works two fold. First it drops the air temperature of the intake where it injected, meaning again denser air, and second durring combustion it breaks down and delivers more oxygen to the combustion process, which again adds more power. Because of the pressures involved though, this doesn't work with the relativly low pressure diesel combustion.|
It is possible to use nitrous oxide on a diesel engine, in fact it's fairly common in the world competition diesel vehicles, sometimes in addition to water-methanol injection or propane injection.
Also, though, if one is intending to use nitrous oxide on an engine, its a good idea to have a secondary fuel system to add extra fuel to the engine at the same time as the nitrous is being injected, to help keep the air/fuel mixture in the ideal range.
Sumer - May 25, 2007 12:33 AM (GMT)
You'll see why I said it's not for diesel's when you said "sometimes in addition to". N2O doesn't give enough of a power boost to warrant all the added weight without needing even more extra stuff, not with a diesel at least.
In fact I'm pretty sure diesel N2O injection doesn't work at all without Propane injection already installed to bring the burn effecnency up.
I also wrote it that way to discourage people from using it, because a lot of people will go watch sopme stupid movie like "The fast and the furious" and think they can apply it to say a tank engine. Outside of piston powered propeller engines for aircraft, putting N2O injection on a military vehicle is a stupid thing, it increases wear, increases weight, and adds a small ammount of power that's limited by the ammount of space it takes from your fuel capacity. Civil engines for cars and racing are different, but that is by far more rare then the tanks always being designed. This is here to correct the people who believe adding 1000hp to an engine is easy, or claim PMT as making it easy.*
It all comes down to the same reason I didn't elaborate very much on forced induction. I could have explained the differences between supercharger types, clutching systems, and all that, but why bother? I'm the only person who uses a roots blower on a tank engine, and I'm probably the only person who uses a dual turbocharger-supercharger system.
*By the way, what's written here applies for all times. You won't get signifigant power increases from 2050 tech over 2000 tech if you're using a piston engine. We've reached a limit at what we can do and without going to a completely new design such as a rotary or a gas turbine, you're screwed to the old "no replacement for displacement" mantra.
ChevyRocks - May 25, 2007 01:33 AM (GMT)
Now that I did some more research, it appears the intent for using nitrous oxide on a diesel engine isn't exaclty the same as it would be with a gasoline engine.
Evidently in modifying a diesel engine for racing, it's fairly easy to cause the engine to run excessively rich. One way to help counter this is by adding a nitrous system, which adds more oxygen and brings the air/fuel mixture closer to normal. This makes the burn much more efficient, which itself adds power to the engine, combined with the cooling effect on the intake and lowered exhaust gas temperatures.
So it is possible to run nitrous oxide without propane or water/methanol injection on a diesel engine, but it is only practical within the confines of competition engines where outright power is the most important thing. This is entirely not the case for a military engine, because you wouldn't need to balance out excessive amounts of fuel.
Sumer - May 26, 2007 06:51 PM (GMT)
A Breif guide to APU Boosting:
It occured to me today that APU boosting is one of the most widely ignored, but potentially important aspects of an AFV drivetrain, so I decided a breif guide to it might be in order as a tack on to this one. So let's start.
What is APU Boosting?
In short, APU boosting is the practice of using the auxilliary power unit (APU) to boost the time to power of the engine. It takes several forms, and operates differently depending on the engine used, but generally speaking it is designed to bring engine to it's optimal power quickly. Now you may say to yourself, or me, "Well Sumer, you're an idiot! Engines always have power!", but you'd be wrong. Engines operate with a power and torque curve, which means that unless the engine is at it's peak power within a narrow part of it's RPM limit. Tanks and other AFVs often use the transmission to adjust the actual speed, and keep the engine within the peak performance part of it's powerband. Generally speaking, the flatter the powerband, the better for performance. There are cases where this is not the case, but I'm not entirely sure the disambiguation matters for NS. Now there are two ways to flatten the powerband, that is to make it's peak, or close to peak power output cover as much of the engine RPM spectrum as possible. One way, which has seen use in racing, has been to provide the engine with both a supercharger and a turbocharger. This was discussed above, and was the primary reason one of the arguably most powerful and fastest rally cars ever designed was banned completely from competetion. The problem with it however is that it leads to plenty of mechanical issues, especially with diesel engines which are lower speed then simmilar sized and powered gasoline engines (Although lots of marine diesels use it), and is completely useless with gas turbines. So the second option is APU boosting, which can be used as long as their is a sufficient APU system installed under armour (If it is an AFV).
How does APU boosting work?
There's a few ways it works, but I'll start with how it works with a typical turbocharged diesel engine in most AFV applications. In simple terms, the APU is used to boost the exhaust pressure and temperature so that the turbocharger turbine which is in the exhaust system, spinns up faster. This essentially eliminates turbo lag (As described previously) in that the APU, which should already be up and running, is providing the exhaust pressure to get the turbo spun up. This means that the APU has to be fairly close to the engine however, and definetly has to be within the armour of the vehicle. Gas turbine based APUs are ideal for this, as they provide the most exhaust gas pressure for the size, but they eat fuel quickly. A small piston or rotary APU however could provide the needed exhaust quickly with a well designed exhaust system, albeit slightly slower then the gas turbine. It's important to remember however that this doesn't do anything for engine start up time, it only improves the engine's time to power. While an unboosted MTU 870 engine (the series out of the leopard two) may start and run in two to three minutes, it will take six to eight minutes more to warm up to power depending on the environment. APU boosting the engine will still take two to three minutes to start up and run, but within that time frame it will have quickly warmed up to it's peak power because the turbocharger will be feeding it tonnes of air from the start.
But how does it work with gas turbines? Well, it does and it doesn't. A well designed APU system can be used to force it's exhaust gasses into the gas turbine and help get it spinning up faster, which will reduce start time. The problem is that either the gas turbine has to be small, or the APU has to be big, otherwise you won't be seeing much of a reduction in start time. There are alternatives, such as the system I believe being included in the M1A3 Abrams with the UAAPU inclusion. Basically, the idea is to use the APU to provide power to a seperate forced air induction system to feed the primary gas turbine. In simple terms it's a turbocharger for the gas turbine powered by the APU. This has it's upsides and it's downsides. Firstly, what it does is forces more air into the gas turbine faster, which reduces the time it takes to spin up and get running. The problem is that the faster the gas turbine spins up, the less the effect of the APU boosting, and in fact after a certian point the APU system will just restrict the air intake of the gas turbine, reducing it's power. However, if used for startup, it should reduce fuel comsumption for the startup process of a gas turbine, and bring it to power speed quickly.
There is a breif introduction to APU boosting, I hope it helped.
Macabees - May 27, 2007 03:11 AM (GMT)
I think the Block III for the Abrams (M1A3) was canceled in the mid-90s. The M1A2 will be introducing a lithium-ion battery whenever this battery is ready for production. But, AFAIK, it's less for APU boosting and more to reduce fuel consumption of the AGT-1500 when the engine is idle, and to allow the tank to use the sensors when the engine is off. I know your write-up (really informative, by the way) is specifically for engines and the APU's for engine boosting, but I just left this as a note. The Leopard 2E uses an UAAPU, but I don't know exactly what it uses - I think it's electric, according to SAPA (the manufacturer).
Hogsweat - May 27, 2007 07:28 AM (GMT)
Ill be using this when I design my MBT, thanks a lot!
Vault 10 - June 23, 2007 05:51 AM (GMT)
Well, earlier I've mentioned that (as only natural for a nation with dominating aerospace and no ground vehicles) we mostly use turbines, but now I've finally found something which would need diesel engine. However, not any will do...
Do you know of any type, or something, to make an engine very resistant to water? The engine is likely to operate with air intake very low, possibly damaged, and so it's inevitable that water will splash in the intake quite often, and the air will be very humid anyway. Of course, diesels already provide that to the extent, but I'd prefer to make it even better in this regard.
This will be complicated by relatively small size, lack of space around, and lack of qualified personnel - it's for a lifeboat/rescue boat. So it also should start easily, and be quite reliable, for its week or two of use. In case of choking, it also should tolerate it somehow, not necessitating sucking air from the inside.
Macabees - June 23, 2007 05:55 AM (GMT)
I would suggest taking a look at the MTU diesel engine being used on the Marines' EFV project.
Vault 10 - June 23, 2007 03:16 PM (GMT)
MTU 883? Yes, the power/weight seems good. However, that engine operates in pretty soft conditions compared to lifeboats, and only for a small time to bring the force ashore, so I'd rather just borrow the solution making it compact.
While MTU 880 series are quite tolerable, it probably offers no improvement in reliability over water-cooled engines already used. Well, and, besides, the point is to make an engine design, so I just don't want to take RL ones. Solutions and ideas to make an engine more tolerable to seawater are more interesting.
Sumer - June 23, 2007 03:21 PM (GMT)
A normal marine diesel would be fine. Rule of thumb for continious use and heavy wear on the engine is to make it double the displacement that you would have in a truck or tank for the same power. So, if it's a rescue boat then something simmilar to the engines in fishing boats should do fine.
If it's going to be thrown away after no more then two weeks use, then you don't need to worry about underway maintenence as much, but if it's going to be used for years then you want to make sure it's durable.
Edit: Volvo has your aid if you need generals.http://www.volvo.com/volvopenta/global/en-...s/diesel_range/
Cooling is generally done through pipes that run outside the hull in the water, so it's not an issue of radiators, and those engines are designed to be run in really wet conditions. If you've never been in a fishing boat or smaller commercial boat like that they are generally very wet.
Vault 10 - June 23, 2007 03:33 PM (GMT)
Well, most times it won't even be used apart from exercises. Not really two weeks overall, but about a month total lifecycle, with the actual escape being the last, if it happens. It's a rigid self-launching lifeboat to be stored aboard to let the passengers or crew escape, not a standalone rescue boat.
That's, effectively, a tiny craft (10 tons or so), operated in open sea through storms. Issues involved are quite considerable; I don't want to use interior space as air buffer due to uncomfortable and dangerous effects involved. Well, I guess you remember that scene in Das Boot where the engines choked; it could actually rip the eardrums on some subs, and be worse in event of a lifeboat, if it's given a good engine.
So the point is that the engine shouldn't throw any bad trick when the intake is splashed with water, and skip the cycles, but continue working when the intake is clear.
Well, I've been on small motorized sailing yachts (not really have much time, but I enjoy sailing), so know how wet it can get. However, not this wet, when the thing will actually often be completely "submerged" in a wave. And it should improve the resistance further than usual. Normal lifeboats tend to use interior space as the buffer, though sometimes being separated, but it's somewhat space-consuming for a high-output engine.
Yeah, of course, it's to be water-cooled.
Sumer - June 23, 2007 03:51 PM (GMT)
You don't need high output then.
Best bet is to have a seperate engine compartment, nothing too big, just like a "sealed" box in the middle of the boat or something that can be opened for maintenence. Air intakes and all that will be designed to have various valve systems and splash protection so that anything but complete submergance will not hurt it. Complete submergance is going to kill the engine any way though.
Vault 10 - June 23, 2007 03:57 PM (GMT)
Now, it's about the way to make it survive almost complete submersion... for a moment, but still. Either by not letting water into sensitive parts or by tolerating more of it than usually.
Output has to be not high, but considerable, due to worse conditions here, where it might turn out in wrong waters and need to move by itself some distance, before the supplies aboard run out. The buffer might get damaged. Furthermore, there's no space to make an entire compartment, just a section below the double bottom.
So, is there a way to increase salt water resistance, or just make it live through some temporary lack of air?
Hotdogs2 - June 23, 2007 04:28 PM (GMT)
Nicely done Sumer! Im highly impressed, and although i thought i knew the basics of piston engines this has enlightened me further. Definitely useful, i hope you don't mind if i use some of this info on my version of Mac's Nakil 1A1 upgrades, i wouldn't mind having something slightly more powerful in my version, plan being i redesign the hull in line with something like the Nakil 1A2 without the hull based rounds...should give enough room for extra fuel to keep range the same for the more powerful engine.
So thanks, good job and i look forward to using it in future!
Vault 10 - June 23, 2007 04:45 PM (GMT)
Hey, it's Sumer's tutorial! I don't want to take the wrong credit. I'm just discussing things.
[ Mine will be about ships and later... ]
So, 2 Sumer: Don't take it as if I'm ignoring advice, but here the conditions are so rough that just plain nothing, which isn't a solid thick metal, can be relied upon. Some things which complicate it:
- Freefall lifeboat will be launched from aboard ships up to 60m freeboard, at list angles up to overkeel, 180 degrees. The worst case is rapidly increasing list, where, say, the portside boat is released at heavy list to starboard, where it has to fly fast enough not to hit the side. It means up to 60m/s, or 110kts, or 200km/h hit. Or, in real worst case, hitting the side, not that fast, but the hull will be damaged. So compartment integrity is not guaranteed. Storm weather will increase damage further.
- The boat might have to be launched after the ship has submerged, or in that overkeel case. The hatch might be not closed properly, so the boat may be totally flooded. Buoyancy blocks will let it surface, but it must still start the engine after that, to operate the pump and heat the boat before people inside freeze. Tolerating total flooding is a standard requirement for lifeboats.
- Naval vessels, which have enemy fire as a frequent case of destruction, with possible arsenal explosions, fragments around, and other issues, might have the boat breached, but sometimes with just small caliber fire or fragments. The engine must have the power to operate the fast pumps and create overpressure, sufficient to keep a non-watertight boat with some air inside, even if flooding is continuous. If it fails and it has too many breaches, then at least warm the water, provide forced ventilation, give light to treat the wounded.
- A tanker, which will at best carry oil, and maybe kerosene, poses fire hazard; the boat must have fireproof version. That means moving, all covered in burning liquid, through a pool burst in flames at 1000C. Even a steel hull and syntactic foam insulation wouldn't save it for long. The engine must work to operate the sprinkler system and escape the fire rapidly. It will have half-burned, hot air taken in, and may not drain the internal air - it's needed to keep the people alive, who can't breathe the hell outside.
- In cold water, human has 5 minutes to survive, some of which might be already used up if he reaches the boat after being outboard. Then the person must be warmed and dried. The engine will have good batteries to help, but must start very fast, to rapidly turn the lifeboat into a dry, warm shelter. Even an initially flooded one.
These are only some of the requirements for the lifeboat engine. I'll use two engines on larger lifeboats for reliability. Still, each must be reliable and tolerant. The engine might not have a large air buffer, just the often splashed snorkel pipe to breathe. If it's not possible to make it "skip cycles" through that, at least let it restart fast.
Sumer - June 23, 2007 07:49 PM (GMT)
You can't make a diesel engine run submerged. The best you can do is provide adequate water removal systems and route the intakes and exhaust right so that water does not get in. Beyond that you need bateries. You could do a diesel-electric drive if you want.
Vault 10 - June 23, 2007 08:15 PM (GMT)
I understand it can't run submerged, and I don't want that. It only must continue to run through harsh conditions, like after being submerged, but drained later. It might get partly flooded, and pretty wet.
Or could you clarify what do you mean... Just some situations:
- What will happen if the water gets through the intakes, the final valve stops it, but the running engine receives no air at all for half a second or so?
- What will happen if the final valve fails to act, and a bit of water gets inside the engine?
- Will anything bad happen if the boat is 100% flooded, apart from the intake and exhaust?
"What will happen" means how serious the problem is - is it just choking for a while, or stopping to restart later, or receiving permanent but non-fatal damage, or receiving fatal damage.
The boat won't submerge, it will be on the surface, and have intake/exhaust high enough to receive some air even if flooded inside. That's what the buoyancy modules are for. It's also self-righting. Air will be available, but wet and still not always.
Yes, there will be high-capacity batteries, and they will smooth out lack of power, but they don't have the capacity to run the high-performance pumps for long.
Sumer - June 23, 2007 08:30 PM (GMT)
1: The engine will hickup but if it's diesel it will keep going.
2: depending on the layout of the intake system then a little water won't be an issue, combustion should occur as normal.
3: as long as the engine is water tight, no.
The intake system should be shaped like a T on it's side. Designed to take air in but have a drain area incase water comes in. Exhaust isn't quite as bad, and if designed for the right pressure can be completely submerged as long as the engine is running, a valve in the exhaust can keep water from comming back when not running.
The only way you're going to permenantly harm the engine is if it is completely submerged in salot water, both inside and out, for long enough time to rust enough to cease it. Other then that you could probably leave it completely submerged an hour, drain it, refill the oil and start it up.
The electronics will be a problem. But diesels don't need them that much. Turbochargers will be completely ruined if submerged though.
Vault 10 - June 23, 2007 08:54 PM (GMT)
Thanks, that clarified it. So no turbochargers, got it, though their slow startup was a problem anyway. I also don't want to depend much on electronics... They can be made very reliable, and fully waterproofed, but they aren't necessary, after all, so why complicate it.
Now, some more things. In general, what layout and what if any "extras" would you suggest? I guess inline 6 is quite a good idea, but maybe not. The engine would better be flat enough (within 0.5m high) to fit conveniently into the double bottom, to keep weight low.
Power output should be... well, not sure, but maybe around up to 300-500hp. It should either operate efficiently in a wide power range or be compact enough to put two half-power ones. Also, what about the technology in MTU 890 series? Their small size seems attractive, and 2 is better than one, but I'm not sure if anything from there can be applied here.
Hotdogs2 - June 24, 2007 09:26 PM (GMT)
Yeah sorry about that, Mac pointed that out to me, i think its because i saw the last poster when i looked at the thread, and failed to note the actual author! Sorry about that one. Edited the post anyway.
A diesel will be easier to run through water because it can be waterproofed easily, mainly because it doesn't use any spark plugs. That said how stuff works(source of so much knowledge :D) says you would have to water proof the electrics for the engine for it to continue running underwater, probably important in a boat.
Vault 10 - June 25, 2007 10:13 PM (GMT)
OK, so, let me make the first try.
To give an impression of what is it for, some craft specs.
Freefall lifeboat for transport vessels, capacity 24 nominal, 50 maximum
Fully closed, motorized, SOLAS compliant, steel+CFRP construction
Dimensions: L 12.8m, B 3.10m, H 4.25m, Tnom 1.0m, Dnom 28,000kg
Weight: 16,000kg empty, 3,000kg supplies, 7,000kg fuel oil, 2,000kg nominal passenger load
Buoyancy modules: 20,000 liters of low density syntactic foam
So, the engine.
NCR Heavy Industries DE-120
4-stroke diesel engine
Configuration: Inline 6 [Or take V12? Flat 12?]
Material: Titanium [? I'm not sure, but I need to save weight if possible, and corrosion resistance helps...]
Mass: 500kg [?]
Induction: Natural, T-shaped valve
Fuel used: No.1 to No.3 Fuel oil, marine gasoil, marine diesel oil
Compression ratio: ?
Speed: 1600rpm optimum, 3200rpm max
Power output: 200 kW at 3200rpm, outside temperature 300K
Specific fuel oil consumption: 200g/kWh optimal, 220g/kWh average within 20%-100% output
Specific lubricant consumption: 1g/kWh optimal, no more than 1.5g/kWh
Torque: ? [if needed at all]
Is it right? Anything which would better be different? I mostly just put guesses.
Sumer - June 25, 2007 10:52 PM (GMT)
You'd be fine with aluminium, but making it out of steel regardless of the weight might not be a bad idea. Makes it more rugged.
You only need an I6, you might even be able to go as low as an I4 8L engine.
I wouldn't worry about compression ratio.
Your torque would be between 10% and 20% more then your power output in horsepower.
Vault 10 - June 25, 2007 11:05 PM (GMT)
|You only need an I6, you might even be able to go as low as an I4 8L engine.|
But I4 is unbalanced, and particularly bad in this aspect.
| You'd be fine with aluminium, but making it out of steel regardless of the weight might not be a bad idea. Makes it more rugged.|
I don't need long life; would it affect engine survivability? Titanium seems attractive due to no risk of corrosion creating problems for an engine which might be neglected and just stay there for years not even checked. For aluminium, it has some tendency to react with seawater under some circumstances.
What about other specs? I also wonder which speed would serve the purpose best. Another question is how to reach maximum range of efficient operation. More than 200kW could be useful, but if it doesn't hamper slow operation - ~25kW will be needed constantly.
Sumer - June 25, 2007 11:31 PM (GMT)
Maximum range will depend more on any number of things I can't answer for you, including your gearing, propeller, hull form, sea state, and other stuff.
The bottem line is, you can't have an engine that will run if left alone for even years at a time and not maintained. It's impossible.
Honda makes engine blocks out of aluminium already, I don't see a problem. Maybe some form of aluminium alloy. But I still believe steel is your best bet. Titanium will flex too much and require extensive reengineering of the block design, which will hamper any number of your needs, especially low maintenence.
Balance is a funny issue with engines. If you have more then one cylinder, it can easily be well balanced. Four, five, six, eight, ten, they're all able to balance great, especially with marine engines. General rule of thumb however is that more cylinders means more balance, at the cost of smaller cylinders. This is great for things like a Ferrari where that gives more speed and power with less strain and minimises vibrations to almost nothing, but on a diesel, especially a marine diesel, it's bad. More smaller cylinders here will reduce your engine's ability to injest seawater and just hickup. the difference between a I4 and a V8 for instance, if they're both 8L displacement, could be as dramatic as 1L of seawater causing complete failure in the V8, but only a minor hickup in the I4. I4 and I6 are the ideals for smaller marine diesels like this, but it doesn't matter as much when you get massive V18 engines in like submarines that have plenty of displacement to spare.
Vault 10 - June 26, 2007 07:35 AM (GMT)
| Maximum range will depend more on any number of things I can't answer for you, including your gearing, propeller, hull form, sea state, and other stuff.|
I mean not the craft's range, but engine's. Retaining, say, 220g/kWh consumption, even if working at 10% output (20kW out of 200).
|The bottem line is, you can't have an engine that will run if left alone for even years at a time and not maintained. It's impossible.|
Well, but they do, somehow... Lifeboats often get neglected on cargo vessels (like if anything didn't), but still work. And the thousands of tanks from T-34 to T-72 standing in reserve with only checking each 5 years apparently aren't there just to stand.
Of course, what is meant is not just stopping it and leaving for years, but rather preparing for low-maintenance operation.
Or, in general, what specifically is the problem which won't let a diesel left alone for some years to work?
| the difference between a I4 and a V8 for instance, if they're both 8L displacement, could be as dramatic as 1L of seawater causing complete failure in the V8, but only a minor hickup in the I4. I4 and I6 are the ideals for smaller marine diesels like this, |
Well, then inline 6, I guess, a narrower prolonged engine will be good for the structure. BTW, how will bore/stroke ratio affect this? Will wider bore with shorter stroke be better, or not?
Sumer - June 26, 2007 11:26 AM (GMT)
That will be entirely dependant on how often it is maintained, how it is built, and how underpowered it is, in a sense. If it's able to say put out 600 shp, but is rated at 350 shp, maintained regularly, given a steady supply of fuel, and designed for long running condition, then you can easily run it for days, maybe as high as two weeks. That's just a hypothetical set up to let you know, I'm in too much of a rush to convert kW to hp right now so I'm pulling figures out of my ass.
Fluids. Like all piston engines (And this is even worse for a wankel by the way) the fluids break down. To prepare an engine for long term storage it's left in what's called dry storage, meaning it's literally drained of every fluid. Then they can keep it as long as they want, but it will have to be reoiled, refueld, in many cases it will have to be taken apart and given a somewhat extensive overhaul, and then run. Those Russian tanks in storage for instance are overhauled every few years and run a few times, then dried up and packed away. Lifeboats on container ships or other ships that opt for an enclosed lifeboat instead of the more modern life rafts, are maintained in port every time they sit in for supplies and stuff. Sometimes they're even maintained at sea. It only takes a few hours every couple of weeks to do.
Bore stroke won't really mean anything here. All that matters is that it has the individual cylinder displacement to take punishment. You may want to increase stroke over bore to get the desired displacement and save space around the engine though, as a lot of marine diesels of this size tend to do.
Vault 10 - June 26, 2007 11:50 AM (GMT)
|Fluids. Like all piston engines (And this is even worse for a wankel by the way) the fluids break down. To prepare an engine for long term storage it's left in what's called dry storage, meaning it's literally drained of every fluid. Then they can keep it as long as they want, but it will have to be reoiled, refueld, in many cases it will have to be taken apart and given a somewhat extensive overhaul, and then run. |
Of course, refueling and reoiling will be in order. If you mean just that, then OK, I guess it's possible to do while working on batteries.
For overhaul, how can I avoid these cases where it's needed?
|Lifeboats on container ships or other ships that opt for an enclosed lifeboat instead of the more modern life rafts, are maintained in port every time they sit in for supplies and stuff. |
Actually SOLAS rules require enclosed lifeboats on all large international vessels. Life rafts have been known for very long, but due to poor reliability of this method are only accepted as replacement on small or local lines vessels. Since 2004, for bulk carriers it's even required to have not just enclosed, but even heavier and faster-launching freefall lifeboats.
While relying on maintenance is an option, and it by no means is supposed to be cut, having the engine tolerate neglect is still better than not. Anything that can be done to ensure this? Or maybe just enforce a test run once in a while?
| It only takes a few hours every couple of weeks to do.|
BTW, what specifically is included? Is it possible to make the engine as low-maintenance as a car one?
Sumer - June 26, 2007 12:00 PM (GMT)
Keep it filled with the right fluids treated for long term non-use and run it every week for half an hour or so. You can keep it fueld and ready to go indefinatly that way.
And keep in mind changing the fluids takes time and equipment like pressure systems and air compressors that will mean you won't have much room for people. You'd need to effectivly cram an entire mechanic shop into this thing, plus be sure to always have the mechanic onboard when it deploys.
No need for a test run. Just have the ships engineer walk over to it once a week, start the engine, let it run 15-30 minutes, and then go back to his regular duties. He can do it on a coffee break.
It will be lower maintenence by far. Car engines are run on a regular basis though and so don't need storage care. But all your mechanics need here to maintain this is a basic set of hand tools and a few other things like a timing gun.
Vault 10 - June 26, 2007 12:14 PM (GMT)
|It will be lower maintenence by far. Car engines are run on a regular basis though and so don't need storage care.|
Well, you can leave a car for a year, get back and start it, even though not instantly, but quickly and without any special tools [may depend on car, though].
| Keep it filled with the right fluids treated for long term non-use and run it every week for half an hour or so. You can keep it fueld and ready to go indefinatly that way.|
What about making it start up regularly automatically, say, biweekly, if not checked manually? Through auxiliary electronics, I mean. No, doesn't mean it won't be maintained, but Murphy's Law says if it can be done wrong or neglected, it will.
I guess some non-vital electronics, which only supplement normal manual control, won't hurt.
By the way, back to the efficiency curve. So how good can it be done? Can engine rated for 200hp optimal (say, 210g/kWh or 155g/hp*h), 300hp maximum, work efficiently at 30hp? How efficiently, and how can it be improved?
Sumer - June 26, 2007 02:08 PM (GMT)
If you do that to a car any good mechanic will shake their head at you. Leaving it for a year and the oil and fuel break down and ruin the engine. What car collectors do is put addatives in the fuel and oil that keep ir from breaking down for that long. One of the bad things about diesel is that it's not that easy to do with it as opposed to gasoline.
You could do that. Although you'd want certian electronics anyway, starter system, glow plugs, fuel injection managment. So it won't be an issue to add a small computer that starts it and runs it on a regular basis when not in use.
Effeciency is a funny thing, it depends entirely on so many factos I honestly can't give you a concrete answer on curves for NS stuff. It's really engine specific. Power is just as odd. You can't just say it will be so effecienct at such a power, it's more relevant to RPM. With a 300 shp engine for instanstance, you're not going to bring it down to 30 shp without really eating up the fuel just to keep the cylinders going so slowly. Your maximum effecient area is within a range of the RPM band where both torque and power are close to eachother. The thing is, lower speed = torque, higher speed = power. This is why gasoline and diesel engines have different ratios of each compared to eachother. So take two engines with an RPM range of 1000 to 8000 rpm, one a diesel one a gasoline. The gasoline engine will be more effecient in the upper band, around say 6000 rpm, and the diesel will be more effecient in the lower band, around 3000 rpm. Superchargers and turbochargers can mess this up like crazy depending on how they're used, like for instance the Lancia Delta S4 with it's compound turbo system (IE both a turbo and a super) managed to have torque and power curves that were not only identical, but virtually flat through 70% of it's RPM band. That's a good thing for what it did, but not so useful in many applications, like this.
So, after that, the short answer to your question is your most effecient range here will probably be around 3000-4000 rpm, putting out around 300 shp if the engine is rated for a maximum of 400-ish shp.
Vault 10 - June 26, 2007 03:18 PM (GMT)
| If you do that to a car any good mechanic will shake their head at you. Leaving it for a year and the oil and fuel break down and ruin the engine. |
Well... still there are people who do that, use an old second car a month in a year (in another place), and the cars still work. Though I well understand it's neglect, but the point is to know if it will work, not strip of maintenance.
|You could do that. Although you'd want certian electronics anyway, starter system, glow plugs, fuel injection managment. So it won't be an issue to add a small computer that starts it and runs it on a regular basis when not in use.|
Then so be it - the control computer will give the engine a small run once in a while, plus report if any issues arise. Would also do certain things if excessive trim, heel, shock is detected, or damage is reported - open the door, turn on the lights, prepare the engine.
|So, after that, the short answer to your question is your most effecient range here will probably be around 3000-4000 rpm, putting out around 300 shp if the engine is rated for a maximum of 400-ish shp.|
Hmm... OK, clear on this.
And how much is wasted at low power? Does it make sense to put in an APU to work at low power? I guess the APU here would be a small 2-cylinder boxer engine working at constant RPM to put out 15kW electrical or 20hp.
Sumer - June 26, 2007 04:17 PM (GMT)
If you really want just go diesel electric, then power is not an issue of fuel. At lower rpms you'll have to use more fuel to ged the deatonation to happen with lower compression that will be in effect. It will certianly be less fuel per minute then at a medium or high one, but it will be more proportionally.
A lot of fishing boats, who's engines must run for weeks without stoping and are usually in the 400-600 shp range will use a small 2 cylinder generator for power supply of things. So they're not hard to get away with. Alternativly you could just design the engine with it's computer to shut down cylinders. This has problems in that it keeps the wear and tear on the engine, and uses more fuel per cylinder, but overall uses less fuel. But I don't see why you'd need it to run at such low power anyway.
Vault 10 - June 26, 2007 05:39 PM (GMT)
|Alternativly you could just design the engine with it's computer to shut down cylinders. |
Hmm, that's interesting. Is it applicable to a semi-mechanically controlled engine, meaning, will I retain the ability to run it on pure mechanics?
BTW, about breakdowns of liquids... Would it make sense to use fuel oil no.4, to reduce losses with time?
|But I don't see why you'd need it to run at such low power anyway.|
For stationary operation. Just to keep the heating, ventilation, desalinization, lighting, signals alive.
Average 75-kg male human can survive on 8MJ/day of food and 0.5l/day of water for significant periods of time. Food can contain about 20MJ/kg, which, with 32kg/person supply, ensures 80 days of survival, not counting fishing and internal supplies. At the economic speed of 2.5m/s (5kts), taking 20kW to sustain and so 110kg/day, this allows to reach 10,000km (5,500nmi) in 50 days, which even in NS world should be sufficient to get to coast or at least a shipping line, with 30+ days waiting period left.
I'm really not sure if I need it, though, or if I need the 120kW engine. However, providing, even though for only 10 days, this power, it could move the craft at 5m/s (10kts), for 4,000km/2200nmi, to provide faster transport when there's coast close enough.
True diesel-electric, though, might actually be more practical here. Just that certain concerns about reliability might arise. Also, though it could achieve major fuel savings by sailing submerged, that complicates detection too much to consider. OTOH, satellite network density makes transmission from a properly equipped boat likely to be received anyway.
I'd also prefer to keep the total craft cost below half a million, to keep it not just good, but cost-efficient, meaning that, for average accident rate and person's economic contribution, installation of the boat would bring net economic benefit. While lack of that wouldn't be a problem for V10, convincing on international scale would need economic arguments. Electric systems can easily bring cost up.
Sumer - June 27, 2007 12:13 AM (GMT)
It depends how you design it. In theory you can simly have the computer not inject fuel into the cylinder you want to shut down, and then the only thing that will be needed is electronic fuel injection, all else will be as mechanical as need be.
All fuels and oils break down over time, it can't be avoided. The absolute cheapest and most effecient way of avoiding this is to change the fuel and oils on a regular basis. Luckaly for oils and other lubricants you don't have to change them very often, maybe once a year if you want to keep on top of it. Fuel on the other hand no matter what you use needs to be changed more frequently.
Why would your lifeboat sail submerged?
The engine in your lifeboat won't be too expensive depending. The engine you want, or have expressed wanting, will be quite expensive in the six digit price range. But you can easily go with a more realistic smaller engine in the $8000 range.
Vault 10 - June 27, 2007 12:23 AM (GMT)
|Why would your lifeboat sail submerged?|
Well, not really that it would, but that's a potential way to save fuel at higher speed. More efficient propulsion, less drag, and less waste due to instability. However, not really a good one, since it should stay on surface to be noticed.
| The engine you want, or have expressed wanting, will be quite expensive in the six digit price range.|
Hmm... Just for 160hp optimal, 270hp top, made of steel, inline 6?
While it's marine, I don't get why would it be costlier or as costly as, for instance, a titanium-ceramics 2000hp one with much more complex design.
Sumer - June 27, 2007 12:26 AM (GMT)
No for the engine originally posted, the I6 6L one.
Marine diesels come with an array of crap on them, including gearing and bilge systems. My Crower cycle engine, for instance, is the price for the engine alone, no extra systems like electronics and gearing and bilges, just the engine block and stuff attached to it to run. That is, oddly, the cheapest part of the engine system.
Vault 10 - June 27, 2007 12:35 AM (GMT)
Well, what I posted is it - 200kW maximum, 120 optimal/sustained.
But six figures? An entire truck with 270hp engine easily fits in five figures; even with 540hp one. Neither do other marine diesels cost like $1000/kW (even turbines are cheaper!). Why would a dumb low-performance diesel cost that much?
Here the electronics are minimal, gearbox is fixed-speed.
Sumer - June 27, 2007 12:52 AM (GMT)
Because they're designed to be run indefinatly. That adds a lot to the cost.
And once again, I am basing that off your original post nregarding the 400-600 shp engine. I am yet still too lazy to get off my butt and convert kW to hp because I know hp much better then I know kW.
Vault 10 - June 27, 2007 01:05 AM (GMT)
| Because they're designed to be run indefinatly. That adds a lot to the cost.|
But not that much, for medium-speed ones. They go five figures for the power. And this doesn't have to run for many years, just a month at low power.
|And once again, I am basing that off your original post nregarding the 400-600 shp engine.|
Well, changed now, to 160-270hp.