has this ever been done? I think a few poeple tried when rotaries first gained interest. Can it be done with todays technology ?

 

It might be a good idea, but the issue is that youd need very very high compression for it to work, and obviously direct injection.

BTW, diesels dont work by knocking, they ignite by squirting the fuel into realy hard air. But the thing is diesels do knock from time to time and are built to take it... whereas a rotary likes to spit seals out.

Maybe if the apexes of the rotor were somehow stronger and braced the corner seals more, it would work, but Im not sure - but thats only an issue if ou can even get the compression in the first place.

Also, diesels by design cant burn the fuel fast enough to rev very high in a piston motor, at least - but a rotor spins once for each 3 spins of the e-shaft. So, that might help in some ways, being 1/3rd the speed of the output shaft.

Frankly Id be more interested in gasoline direct injection (and some dishes or toroids in the bathtub for stratified charge super-lean running to help with mileage) and finding a way to strengthen the apex seals, as well as making the engine longer along the e-shaft to help improve geometry (and surface area to volume ratio) with a rotary than switching to diesel, but thats just me.

 

John Deer had a Stratafied charge rotary engine powering electric generators some time ago. They had a 200 hp model, and a 750 hp model.

and for those who don't know. Stratafied charge means that the engine draws in a very lean mixture and then at top dead center, it sprays fuel through an injector onto a glow plug. this rich region in the combustionchamber ignites, and then the flame front proceeds thru the chamber and consumes the lean mixute.

Its very much like a diesel.

 

"Maybe if the apexes of the rotor were somehow stronger and braced the corner seals more, it would work, but Im not sure - but thats only an issue if ou can even get the compression in the first place."




It would be nice if the apex seals are built with the rotor itself. That would eliminate seals popping out of ther groves.

 

Curtiss-Wright built a diesel rotary in the early 70's. It wasn't a true diesel though as it still used spark ignition and had a low compression ratio. It was direct injected though. Rolls-Royce also built a diesel rotary engine that used 2 different sized rotors. The larger rotor was used as a supercharger for the smaller rotor. It too used direct injection but was compression ignited. The biggest issue was with starting it.

Freedom Motors currently has an engine that they say can run on diesel. It too uses low compression at 8.5:1 and is peripheral ported. It is also air cooled. Theirs does not use direct injection. It uses (low pressure) throttle body injection. It's actually somewhere around 70 psi which is low for a diesel. Theirs also uses spark ignition rather than compression ignition as the compression ratio is too low. They start theirs on gasoline and then switch over while it is running. No word on power output.

Diesels use direct injection since compressing air only makes far less heat than compressing air and fuel at the same time. Diesel fuel injectors are designed very differently than gasoline fuel injectors. They spray out of several orifices. How many depends on the design of the system used. The new Pump Duese VW systems use a 9 hole injector that fires 5 times per compression event at extremely high fuel pressures. The previous VW systems had lower fuel pressures (still several thousand psi) but had 5 hole injectors that fired twice per compression event. Then you also have the CDI systems and the older mechanical injection types. Al nozzle designs were very different.

It is due to these new injector designs that have improved diesel engines. They don't inject fuel over nearly as a long a duration as gasoline engines. They also need to better control where the fuel goes hence the multi hole injector nozzles. They want a fairly even burn for max efficiency. Direct gasoline injection is trying to get very close to these types of systems in many ways.

If we inject diesel indirectly such as in conventional fuel injection systems, it will heat up faster and preignite compared to direct injected diesel. One way to offset this is to use a lower compression ratio. This is why it works for freedom motors and why it also worked for Curtiss Wright. The downside is that now you have lost the high compression advantage of diesel and are making less power than gasoline. That kind of defeats the purpose of it.

Diesel isn't rated in octane like gasoline is. It is rated in Cetane level. I wish I understood this. It does have an octane level though as this is nothing more than a resistance to ping. On diesel it is actualy very low. Somewhere between 20 and 40. The slower burn rate of it still makes it useful and it contains more btu's of energy that gasoline. It is just very critical how it is injected. This is also true of direct injected gasoline though and we are figuring out ways to get it to burn leaner and leaner without detonation.

Basically there are 2 ways to make a rotary run on diesel. Neither of them will be easy. The first way is to keep it low compression (but still higher than standard fuel injection), inject it at a conventional gasoline location and use spark plugs to ignite it. You definitely won't get a factory ecu to control it. This way will not be very fuel efficient or powerful compared to proper diesel compression ignition but this may not be much of an issue if you wanted to run on waste vegetable oil that you can get for free.

The other way would be to find a way to use diesel fuel injectors, direct injected and timed properly. A true diesel system does not use a throttlebody. It always gets a full supply of air. You just alter fuel quantity. The problem will be with the location of the injectors and modifying a diesel fuel pump. Then you'll have the issue of starting it which supposedly isn't easy. If you can find a way to make this work, there is still no guarantee that you won't blow it all up. Diesel is not detontation. It is a controlled burn.

My big questions is what would happen if you tried to run diesel fuel through a conventional gasoline fuel injector? Ignore everything else. Can the injector do it safely?

Hopefully this helps your questions somewhat.

 

A friend of mine did this to a 12a in the 70s. He used a turbo to raise the compression and it ran fine as a true diesel engine. The biggest problem he had was spooling the turbo before starting the engine and unfortunately his funding was cut before he devised a reliable method. Theres a picture of his engine floating around somewhere, it may be on the internet by now.

 

rotarygod: Cetane rating is a measure of how long after injection it takes for the fuel to light off... higher cetane means quicker lightoff, which makes for smoother more efficient running. And can increase the maximum RPM the things will run at before being limited by how fast the fuel burns. The test is sorta like octane, with a variable compression engine and two reference fuels used... only fuel injection's set at 13deg BTDC, and compression's adjusted until it ignites at TDC.

 

ok, ummmm, where to start.....no offense man.

The reason diesels use direct injection is because a diesel is a compression ignition engine rather than a spark ignition engine. It really has nothing to do with the charge heating faster with fuel in it(which is backwards, it will take longer to heat with fuel in it b/c of the increased heat capacity offered by the fuel).

Diesel fuels have lower octane numbers meaning they will burn faster...The idea is to minimize the delay time between when you inject diesel fuel X degrees BTDC and when the fuel finally begins to burn (this time is known as the delay period The idea with gas engines is to raise the octane rating and beat the delay period with the flame front b4 the fuel knocks. Yes it slows the speed of the flame front, but it slows the rate of the chain reactions that is detonation more significantly).

You are right that diesel is a controlled burn, but controlled differently. Using the delay period(which changes for different pressure/temperature curves of the combustion chamber), you can calculate when to inject the fuel BTDC to create the maximum power, just like spark timing. All that fancy injection stuff you were referring to is very interesting good info.

The john deer had higher compression than your standard mazda i believe. I'm not 100% but from seeing a rotor, it would appear so. I do know that they made they're own rotors and housings and didn't get them from mazda. The indentation in the rotor face was shaped like a tear drop to best accomodate the sprayed fuel. The compression ratio of a rotary engine is generally controlled only through the volume of the indented chamber in the rotor face. Smaller indentation, larger compression ratio.

1 other thing, you can have a manifold injected diesel, however it woudln't be praticable because there has to be many conditions just in sync to get it to run right and at its maximum efficency.....which mostly has to do with the allignment of the planets.....JK It would only work for constant speed, constant ambient temperature, contsant inlet pressure, and constant compression ratio. that would involve matching all the above said conditions with a specific fuel's cetane rating to acheive the best results of ignition at just the correct moment. But again, its constant speed, so you can't rev, you can't bog down much...otherwize you loose efficiency or blow up the engine all together!

I dont' mean to knock on you too hard rotarygod....I just want to have the right information(or the most correct as it can be) posted here....and everywhere on the internet for that matter..... The rest of what you said was very interesting and i'm glad you typed it up.

I also apologize for any spelling or grammar mistakes, Mack trucks didn't hire me because I can write a good book report.

 

Diesels usually have very low rpm ranges. Given such, apex seals could be engineered like the old 6mm apex seals from the 70's. Those would hold up to low rpm and knock without a problem.

 

Nevermind. It's not worth the effort.

 

I just wanted to say that there is some very well written responses in this thread. I had an oppurtunity to see some pictures of diesel rotary engines. There were some that were in the 2500hp range. Remember that these were massive though. I believe that it was the old John Deere warehouse.

Z

 

Diesel fuel won't directly light from a spark. Well, not as a liquid. The key to igniting diesel fuel is atomization, thus the use of higher fuel pressures, more injector holes, and firing more times per combustion event. I saw on some TV show they had a big container full of diesel fuel, and they took a propane torch to it. It didn't light.

 

Diesel fuel won't directly light from a spark.

The way the Freedom rotary ignited the diesel with a spark was to run the air/fuel charge through the rotors (thus cooling them as well) to atomise the mixture. This is why the engine had to be started on conventional spark ignition fuels (gas, lpg, etc.)

A turbo or supercharger could do it as well, but only when compressing- ie, engine under load for the turbo).

So, a Lysholm supercharged Miller cycle diesel rotary with a fuel heater for start-up?

 

Curtiss-Wright, John Deere, Freedom Motors, have all ignited diesel fuel in rotaries by using spark plugs. The highest compression ratio that was used by any of then was 10.7:1. There is only one company that makes a diesel rotary that uses a glowplug and that is PATS. It it is a single rotor 18 hp auxiliary power unit (apu) for small business jets. It is currently in production.

 

could water injection help raise the compression ratio, the water wouldn't compress and the air would (i think?) still compress. Because the water is taking up space in the combustion chamber, it seems the compression ratio would be increased this way. Although it would **** with the burn and combustion itself, but maybe in a more efficient and more powerful way. Also, if the ignition of the diesel fuel is a problem inside the combustion chamber, the speed of flame spread can be increased by adding some hydrogen to the intake manifold. The hydrogen can be had from a small reaction chamber that uses electrolysis to seperate water into hydrogen and oxygen, then route it to the intake. Maybe a solar panel could help recharge an extra battery that supplies the power to the pulse generating circuit that supplies pulses at the right frequency, voltage and amperage to the stainless steel reaction chamber producing hydrogen (or brown's gas) then on to the intake manifold. idk, just trying to be an innovative thinker, plus a BIO-diesel rotary engine with hydrogen combustion assistance would probably be a pretty bad *** setup if done correctly (which is how I like to try and do things). I also was thinking, maybe the engine can start on hydrogen using the aux. battery for the electrolysis, then as the engine is started a supercharger of some sort could compress air into the combustion chamber (increasing the compression ratio), the supercharger could supply the compression ratio for low load conditions, then a turbocharger can take over for high load compression ratio. all this sounds like a lot to deal with, a lot to break. and probably hard to troubleshoot, maybe it would be worth it though?

 

Right, I wasn't meaning to imply that you couldn't ignite diesel fuel, I just was trying to point out what I consider an advantage to diesel and show the importance of fuel atomization for diesel ignition.

 

does anybody have any specs, pictures or websites for that matter of any diesel rotary engines, such as that airplane company that is making them, or any other websites that show it. my friends are rebuilding one and were talking about adding rotors to the engine, like adding 2 engines together, and i brought up the idea of making one a diesel rotary engine and they said it couldn't be done at all. as i was thinking more about it, it is very possible, a lot of engineering and fabrication but still possible. like someone said before, the seals would need to be really beefed up, and the housing should also be stronger too. where the 2 plugs are, fill the second one in and use the first one on the rotation for the glow plug. also turboing it will bring the compression right up there. but like someone else said before, starting it would be a pain in the butt., but you could start it with an electric motor possibly. just throwing thoughts out in the wind.

 

Anyone who says that deisel won't light from a spart is wrong. I don't know if this would work on the "lean burn" carb engines after 80 but the 80 and before engines with thermal reactors would run on deisel. I ran out of gas near a rest area and bought 5 gallons of deisel off a trucker, and drove allmost 50 miles on it in. It smoked some, stunk, and felt like it was missing allot of power but it got me to a gas station. Doing this was a well known fact, I have an early "mar 1979" issue of rotary rocket magazine where they talk about this.

 

Most of this is hearsay but the crowd may find it interesting. I was working for the the UN in Jerusalem a few years back and one of my coworkers was an Australian Army Major Proudfoot. Cam was an Armor officer who had worked in R&D for the Australian Army. For several years he had been invovled in efforts to develop a turbo-diesel powered rotary engine for use in tanks.

When I asked him about how well it worked he said it didn't. Basically they couldn't get the engines to properly seal between the rotor and side housings at the kind of pressure that you need to run a diesel engine at. Also keep in mind that their idea of reliability might be alot more demanding than an average car owner would be concerned with. I don't remember what company they were working in conjunction with.

He also added that he always liked the design and it looked promising, but that they just couldn't get it to work reliably. Maybe with more modern technology, I think he worked on this in the 80's, it might be possible to work today.

Cheers,

Peacedog

 

i'm thinking a significantly larger rotor and larger apex seals (in fact, larger seals, period) on a fully peripheral design should do the trick. at least, that's what i came up with ...

 

I don't really see what the problems would be with generating that much compression. it seems like the the cylinder pressure generated by a high HP turbo engine would far exceed the pressure generated in compression by a compression ignition engine.

 

I would like someone to try out some 6mm ceramic apex seals for extreme duty rotaries.

Early Mazdas used 6mm carbon/alum apex seals and gained a little bit of power going to 3mm seals (5-10% on the race engines, I forget exact #)

So, how does peak combustion pressure vary between diesels and gas engines?

I would think a spark controlled diesel would not be as prone to pre-ignition and detonation as a glowplug/compression/lean-out igniton diesel, though I bet diesel fuel varies much more on volatility than our octane rated gasoline so timing would have to vary.

So (if you could contol it) controlled burn peak combustion pressure would be a funtion of CR and HP whether gas or diesel?

 

Modern electronicly controlled dirrect injection diesel engines are not prone to preignition.

Using spark ignition for diesel engine would negate most of the benefits of diesel in the first place.

 

Propane would be interesting

 

I have the following from an old magazine