rotarygod

I've talked to the guys at smartplug. I tried really hard to buy a set of plugs off of them but at this time they are only doing projects for the military. Remember, if it has no ignition system, it isn't going to be affected by an electro magnetic pulse.

I've spent some time thinking about how to do a diesel rotary off of true compression ignition rather than spark plug ignition and it would take a high degree of custom work but could be done. It would be indirect injection rather than direct. I've got my reasons for this. It having already been done by PATS as a small jet apu and the only successful compression ignition rotary in the world being a good reason.

Aseras

well a diesel needs no ignition once it is running. all it needs is air and fuel and it ill run forever.
that's what's great about compression ignition. My reasoning is the rotary already runs hot. I'm wondering if you started on gas or a light gasoline/diesel mix and got to temperature and then switched to diesel or a heavy diesel gasoline mix or preheated the diesel and injected it perhaps post turbo with some PSI you could do a compression ignition rotary 13b.

some of the modern diesels are only running about 12:1 compression with a turbo now. they have a air pump / electric turbo to get them to pressure for starting now.

RX8SaxMan

Well, since I believe the formula for HP is: HP = (Tq x RPM) / 5252
Torque at 4500 RPM is about 408 lb/ft.

ds2000

Doesn't diesel burn purely on high compression? if I'm not mistaken rotaries run at 10:1ish

Interesting figures above though

BlueSky

A diesel rotary would be awesome.

rotarygod

It's hard to describe why a rotary has a hard time at higher compression ratios without writing out a small book so I'll just say that practically speaking, 10:1 is about the usable limit for the static compression ratio. Fortunately for us it's dynamic compression ratio that does all the work so we can take care of this with forced induction. In teh above picture, notice first of all that it is a 1 rotor based on a 13B. The smartplugs are necessary even though there is diesel as the compression ratio is not high enough on it's own to combust the diesel fuel. In fact they actually had to run a lower compression ratio of 8.5:1 on that engine so it would detonate. Instead of direct diesel injection (or indirect injection in a precombustion chamber), they mixed the fuel in just like our engines basically do now and by that I mean in the intake manifold.

When you compress the air and fuel together it is more likely to detonate. While diesel fuel isn't rated in octane, it nevertheless still does have an octane rating. Typically it is somewhere between 20-40. That's it. That means it detonates easier. What is detination? It is an uncontrolled burn where there is no longer a single predictable flame front. Usually many hot pockets will start to ignite on their own and we have several flame fronts colliding with each other. This puts different stresses on the engine and not in a good way. Direct injection changes this. Since diesel fuel burns more slowly, it is more predictable. The flame front is controlled in a different manner than in engines that mix it in the manifold. As diesel fuel starts to ignite, not all of it is injected yet. As it burns, more is added and this controls the flame front expansion. We only burn what we need. This means that less of it is likely to be stuck in random spots in the engine and remain unburned. This makes it more efficient and cleaner. Since we now have control of the flame front, we can now raise the compression ratio higher before encountering detonation. This is actually why direct injected gasoline engines are getting popular. It is much the same control that we desire. You'll also notice that as the years have gone by and control of fuel metering has improved, compression ratios have also gone up. Now you know why. I am of course ignoring many things such as fuel pressure, spray pattern, and fuel timing in relation to timing.

In the above smartplugs diesel engine, they had no control of the flame front and with such a low detonation tolerance, they had to run low compression. This means that while the engine is likely to ignite the fuel more easily in an uncontrolled manner, it isn't as easy to ignite it controllably. The first way to make it work is to keep the compression ratio down. This hurts power but you are still making more power than you are on detonation. The second thing to overcome was how to ignite the diesel fuel. Since it burns slower and has a much higher flash point than gasoline, it takes a more intense spark to set it off. The smartplugs have a very intense burn rate that does the job. That's how that engine works. Unfortunately it probably isn't quite as simple as installing those into a Renesis and then just trying to run diesel. You'll detonate. It isn't terribly hard to make it work though. The other issue with doing it this way is that you lose the benefit of running diesel in the first place. It may have more energy content than gasoline for an equal amount used but the lower necessary compression ratio will undo this. Combine this with the fact that diesels don't have throttlebodies and therefore no intake restrictions other than the valves and this too is another benefit of diesel that is no used.

If you want to see what a properly done diesel looks like, look no further than the PATS apu for business jets. True compression ignition on direct (indirect prechamber) injection. In other words the fuel gets metered at the ignition point rather than the manifold. Here's a link to a page with some cutaway pictures. Scroll down a little bit. Oh yeah, it's air cooled! Brilliant!

http://cp_www.tripod.com/rotary/pg08.htm

BlueSky

Ok, I read through that but I'm still looking for a bottom line. Will it ever be done?

rotarygod

I doubt it. Mazda is too busy putting all of their efforts into developing hydrogen into a viable power source. Too bad it is as of yet pathetic at best but with a few more decades of research and development they'll probably get it worked out. On the other hand they could do diesel right now in the interim...

BlueSky

I read those scanned pages you posted about the Rolls Royce diesel Wankel.

How would a deisel wankel compare to a gasoline wankel in terms of smoothness, RPMs, power, etc.

Thanks.

rotarygod

The rpm range of course would be lower but it isn't uncommon to see diesels go up past 5000 rpm anymore. It doesn't mean they are making much of their power their though but they aren't all like Ford or Chevy trucks which top out at 3000 rpm or so.

Smoothness will depend on the design and implementation. Typically a rotary falls in between a 6 and 8 cylinder piston engine in terms of smoothness (assuming all else is equal) so at a guess it shouldn't be too far off from that as a diesel either. This is affected by combustion as well though and this can change things. Direct injection and Indirect injection in diesel engines can have differing effects on smoothness and power. You'll have to go look those terms up.

From a power standpoint you wouldn't have the peak power that you have on gasoline but you would have lots more torque. Remember that how fast you are is a function of average power over the usable rpm range. A diesel is typically lower revving and makes less peak power but the average over it's useful range can be higher even though the peak is lower. Again with anything, it depends on the design.

You can guarantee that economy will go up. This is true for a few reasons. The first is that the engine will always be turning at a lower rpm due to the required different gear ratio. Fuel consumption is a function of fuel used over time and even a leaner mixture at a higher rpm can be more fuel used than a richer mixture at a lower rpm. The one thing you have to remember is that efficiency changes with rpm and load so it is inaccurate to say "it takes the same amount of air and fuel to make the same amount of horsepower at a different rpm". Not true as there isn't enough info. Efficiency makes that so.

A diesel is more efficient for an obvious reason that diesel fuel itself contains more btu's of potential energy than gasoline. That's all find and dandy on a test bench in a lab but in use it's not quite this simple. The speed at which it burns has a larger effect in practice. A diesel engine is always at a higher "load" than a gasoline engine. That may sound strange but I use the term loosely as I'm really referring to the amount of pressure, or lack thereof in the manifold at anything other than part throttle. A gasoline engine has a throttle plate in the way. This creates a lower pressure area in the manifold that we typically just call vacuum although this too is a little bit misleading. This means that the engine has to work harder to get air past this restriction. This makes our throttlebody a pumping loss. A diesel has no throttlebody at all. It is always getting a full supply of air. Power is determined by the amount of fuel added to the system and this is what is carefully metered. This means the engine has less pumping loss for most of the load range than a gasoline engine. When you are cruising down the road, you're throttle plate is barely open. It's only fully open at full throttle.

Diesels today are direct injected and typically the fuel spray and combustion are better controlled which is also an increase in efficiency. Gasoline engines are slowly progressing and will slowly close the gap but how close they'll ultimately get is still a mystery. We'll find out.

Rolls-Royce's design looks interesting but closer examination shows it to be large and inefficient. Using a larger rotor as a blower is a big parasitic drag not to mention the blowby they'd get internally on the supercharger side between intake and exhaust. This is harder to explain unless I actually show you. That's not easy to do over a keyboard. Since they used spark ignition they ultimately had less efficiency here as well. It was creative though but it was large and heavy for what it did. Then again by the standards back then, it wasn't all that bad.

BlueSky

Wow, thanks for that reply. It'll take me another 3-4 reads for me to digest it all.

juanjux

True, a diesel engine fisically can't rev faster than about 5700 RPMS so you lost one of the key advantages of rotaries.

globi

Diesel engines use direct injection mainly to control the ignition point and they use high compression ratio to ensure that diesel injected ignites immediately after injection. (The faster it ignites the higher its efficiency).
Gasoline engines use direct injection for several reasons but mainly to allow for a leaner overall air fuel ratio by simply enriching the air fuel ratio around the spark plug.

A conventional engine can easily have a higher compression ratio of 16 to 23 which is needed in a diesel application. A rotary can only reach these high numbers with the help of a compressor (static or dynamic).
Rollls Royce used a rotary engine to pre-compress air instead of simple compressor (roots, lysholm, centrifugal) to be able to regain some of the energy in the exhaust gases. Otherwise it would have lost a considerable amount of efficiency.

Btw the reason why Diesel engines have lots of low end torque has mainly to do with its higher compression ratio and the fact that many of them are turbocharged.

Aseras

the turbocharing is a shortcut to run a lower compression engine on diesel. it also allows power devolpment a bit quicker..

globi

Diesels are turbocharged to increase their otherwise relatively low power density. Also turbochargers not only increase their power density but also increase their efficiency. Turbochargers are also more effective on diesel engines than on gasoline engines, since there's no throttle. In addition due to the higher compression ratio gases aren't quite as hot and there's less stress on the turbine.
Lower compression ratio is needed because otherwise these engines simply couldn't deal with the naturally higher pressure in the combustion chamber.

rotarygod

Just adding a turbo and pressure to a diesel does not effectively do anything to it's power level. You can double the boost and you might only get a couple of more horsepower. The diesel engine always have an over supply of air. It's fuel that makes power and more air means you can run more fuel and hence get more power. Of course this assumes you add more fuel. This in turn as with a gasoline engine allows us to get more power from less size. A diesel engine can keep injecting the same amount of fuel regardless of boost and get roughly the same power. Don't try that in a gasoline engine!

I did fail to mention that the higher compression ratio is another reason why diesels have good low end power. It's not actually the turbo that is making them efficient but rather the fact that they can add more fuel that is. Of course a turbocharged gasoline engine makes more power too.

rotarygod

The advantage of a rotary is it's simplicity and lack of moving parts. That's a benefit at any rpm. A disadvatage of the rotary as with any other small engine is that it needs to be revved up high to make any power. Most people think that a high revving engine is a good trait. Needing more rpms to make power results in lower fuel economy and more stress on engine components which ultimately means less overall lifespan than running at lower rpms.

By having an engine that gains low end and doesn't need to be revved up as high, now you've fixed an inherent weakness, not taken away an advantage. The rotary doesnt have a high rpm advantage. It has a high rpm necessity. Give it the usable power lower in the rpm range and now you actually will utilize a benefit of a rotary. Simplicity. Fewer moving parts at a slower speed equals greater longevity.

Don't get me wrong I love the high revving fun nature of the rotary but from an efficiency standpoint in the real world, there is a better way. It may not be the fun way though and that is the whole point of a sports car.

globi

You can only add so much fuel to a diesel engine. Unless you add more air (eg. with a turbocharger) it won't generate more power it will only generate more black smoke.

rotarygod

Exactly.

r0tor

iTrader: (1)

I'd like to see your rotors spin at 9,000 rpms


(hint: the actual rotor speed is 1/3 of what you see on your tach)

auzoom

there was a comment made earlier that US emmisions laws are basically ruling out diesel. Can someone explain why this is the case?

Aseras

because most americans are too stupid to check the urea tank that's going to be required. low sulfur diesel that is sold now won't be allowed or will damage 2007+ diesel vehicles emission system.

auzoom

Cheers Aseras. what about bio-diesel?

rotarygod

Only Daimler Chrysler is dumb enough to use a Urea tank. It will ultimately backfire on them and we'll see them do away with it in a couple of years. Many other manufacturers are not going to need them to meet our new emissions standards. We are going to have a lag time for abot a year or so until the newer engines are brought in. They exist and can do it. The biggest issue has always been that the U.S. has always had high content sulfur diesel while Europe has had low content sulfur which burns cleaner. The new U.S. standard will make ours cleaner than that sold in Europe and all of the diesels have been designed around European emissions standards. Now they have to up it a notch. Instead of matching our fuel quality to theirs, our lawmakers have seen fit to pass them, ignoring of course a myriad of other things that lawmakers always seem to overlook when trying to make any decisions on anything.

Aseras

I'm under the impression that most detroit automakers are going to urea injection/SCR in the short term with the possibility of using a replaceable trap.

GM's options
http://www.gm.com/company/careers/ca...g_out_nox.html

Ford is doing SCR
http://media.ford.com/newsroom/relea...m?release=9996
edit more
http://www.ford.com/en/innovation/te...ionsSystem.htm