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Discussion Starter #1
I'm starting this thread to stir up discussion on a different thermodynamic cycle. It basically takes a gas engine (intake, compression of air/gas, combustion/power stroke, exhaust stroke), and adds fuel after the combustion (like a diesel) to increase the work out from the engine, and further increase engine efficiency.

In terms of theory, this is what sets apart a diesel and gas engine. A diesel engine compresses only air, then adds fuel when the air is heated beyond the flashpoint of the diesel, causing detonation. During detonation, there is constant pressure held in the cylinder while the fuel is added, allowing for all the work to be done at constant pressure. The important part is that the diesel makes its power after the air is compressed, while the fuel is being added.

A gas engine differs in that it compresses air and gas to a stable point, and then relies on a spark to initiate the detonation. For a gas engine, all the energy is added to the system in a split-second detonation, and then that detonation has to push the piston down, up, down again, and then back up again before it get's more energy from the next detonation.

The proposed cycle would go something like this:
a) compress the air/gas mixture,
b) add a spark, causing detonation, [@CV]
c) add fuel post-detonation, [@CP]
d) power stroke,
e) exhaust stroke,
f) intake stroke.

At this point, we know that the temperatures achieved for post-detonation fuel addition will surpass current material melting points.

Please feel free to add your two sense, I'd like to hear from some experienced engine builders to see what they think of the proposed setup, and possible engineered answers to the issues faced.

Cheers from BC, Canada! And Happy Holidays!
 

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I think the Crower 6 stroke is a good example of taking advantige of the heat already created by the first combustion stroke.

I would love to see Big rigs start using it.
 

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The closest thing to this is a DI engine. Direct injection is becoming standard in many vehicles today. Audi started doing it, and now porsche runs it in their 10krpm ALMS spyder. Yes it is better in many ways.

One advantage that a diesel engine has over a gas engine is that there is no throttle plate needed. on the intake stroke a diesel engine draws in a full charge of air no matter if at idle or WOT. Then the engine being limited by the amount of fuel that is sprayed into the cylinder.

On a gasoline engine, if you did the same (removing the throttle plate to allow a full cylinder air charge) and then inject a small amount of fuel, the same as you would to keep it idling, the engine will die. This is because now you have a very very lean A/F ratio and there are many more oxegen molecules between fuel molecules and the flame front will run out very fast and there will be very low, if any, combustion and cylinder pressure which means no BMEP which means no piston getting pushed down the bore.

One of the ways I see to actually make this possible ( a way that I know one manufacturer trying to perfect) is to spray the fuel into the chamber as close to the spark plug as possible, and pico seconds before the plug fires. This may allow the fuel to still be highly concentrated and allow a fast ignition and flame front until the fuel burns out.

A key difference between diesel and gas engine is that gasoline burns at a much higher temp and also at a much faster rate. A Diesel engine can spread its burn out over more crank rotation because the fuel burns slower. You have a much higher overall cylinder volume and thus can have a higher starting pressure and do more work over an amount of crank rotation. This is also a main reason that diesel engines are limited to a lower RPM range. If you get too high up in the RPM ranges in a Diesel engine, the piston speed will be higher than the flame front and the piston will move away from the burning A/F mixture. Once the piston moves away from the flame front, you now have no cylinder pressure directly acting on the piston to "push" it down the bore.

FYI a Diesel and Gas engine DO NOT run off of detonation. In a gas engine, the spark plug ignites the A/F mixture and causes flame propagation and it burns across the bore which increases cylinder pressure to force the piston down.

A Diesel engine contrary to popular belief does not detonate either. The Air in the cylinder is compressed to higher than 400deg F. When the fuel is injected into the cylinder under high pressure the temperature of the air (combined with the transfer of high fuel pressure to relatively low cylinder pressure causes the fuel to atomize) ignites the fuel and again causes the fuel to burn and begin a flame front across the piston.

Detonation is the fuel actually exploding, not burning. It is igniting because of high pressure or temperature in the cylinder reaches the flash point of the fuel and this causes it to ignite from a different point than the spark plug.
 

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Discussion Starter #5
Thanks for the input! First, my bad for burning-terminology.

Exploding CAN be a really fast burn, but has other characteristics to it as well, and doesn't REQUIRE combustion. Touche MRSLAPPY...

I understand that if engines run too high compression (high EGTs), they can have their A/F mix DETONATE before their spark plug fires. Pre-ignition (detonation) could also happen if they have hot-spots or carbon-build up in the combustion chamber.

Also, the direct-injection spray just before sparking sounds good. Only thing to worry about is internal temps over a longer burn like in a diesel engine, but there are fixes to high-temp problems too (water-methanol injection). Should we not be able to spray gasoline pico-seconds before the spark plug fires and continue pulsing fuel after that to keep the flame front burning, and pour more energy into the piston/crank. I believe piezo-injectors or coil actuated injectors should be accurate enough to manage this, no?

I know it's not as easy as bolting something on to the engine, or pouring something into your gas tank to get results, but I am really interested in engine tech, and think that these forums are the birthplace of many good ideas these days. All input is appreciated!

REALLY interesting 6-stroke motor article.... Amazing how old the concept is and yet it hasn't been brought to fruition. I really like how there is no ancillary cooling devices... And the fact that when you expel your exhaust gases, it's mostly water vapour. I wonder how smooth it runs/max RPM/power output from tests. Efficiency would just be a bonus, except you still need to haul around all that water, as you'd need 1 liter of water for every 1 liter of gas.

IDEA:
Has anyone ever tried mixing fuel and water, and directly injecting that? Or having one for fuel, and one for water, to lower the flashpoint of the volatile gasoline, and cool engine temps as well, as I know EGTs are a primary concern when pouring more fuel into a diesel. This would allow a NA engine to run higher compressions too, would it not? By effectively lowering the octane of the gasoline, you could run a higher compression as the A/F mix will "burn" at a higher flash point? Need to tune the setup to the motor, or is it not that easy...

Any Turbo tuners out there that use water-methanol, or NA tuners that run it? Experiences with it? Did it make much of a difference (Turbo/NA)? Any K24's running direct injection out there?
Thanks!




The closest thing to this is a DI engine. Direct injection is becoming standard in many vehicles today. Audi started doing it, and now porsche runs it in their 10krpm ALMS spyder. Yes it is better in many ways.

One advantage that a diesel engine has over a gas engine is that there is no throttle plate needed. on the intake stroke a diesel engine draws in a full charge of air no matter if at idle or WOT. Then the engine being limited by the amount of fuel that is sprayed into the cylinder.

On a gasoline engine, if you did the same (removing the throttle plate to allow a full cylinder air charge) and then inject a small amount of fuel, the same as you would to keep it idling, the engine will die. This is because now you have a very very lean A/F ratio and there are many more oxegen molecules between fuel molecules and the flame front will run out very fast and there will be very low, if any, combustion and cylinder pressure which means no BMEP which means no piston getting pushed down the bore.

One of the ways I see to actually make this possible ( a way that I know one manufacturer trying to perfect) is to spray the fuel into the chamber as close to the spark plug as possible, and pico seconds before the plug fires. This may allow the fuel to still be highly concentrated and allow a fast ignition and flame front until the fuel burns out.

A key difference between diesel and gas engine is that gasoline burns at a much higher temp and also at a much faster rate. A Diesel engine can spread its burn out over more crank rotation because the fuel burns slower. You have a much higher overall cylinder volume and thus can have a higher starting pressure and do more work over an amount of crank rotation. This is also a main reason that diesel engines are limited to a lower RPM range. If you get too high up in the RPM ranges in a Diesel engine, the piston speed will be higher than the flame front and the piston will move away from the burning A/F mixture. Once the piston moves away from the flame front, you now have no cylinder pressure directly acting on the piston to "push" it down the bore.

FYI a Diesel and Gas engine DO NOT run off of detonation. In a gas engine, the spark plug ignites the A/F mixture and causes flame propagation and it burns across the bore which increases cylinder pressure to force the piston down.

A Diesel engine contrary to popular belief does not detonate either. The Air in the cylinder is compressed to higher than 400deg F. When the fuel is injected into the cylinder under high pressure the temperature of the air (combined with the transfer of high fuel pressure to relatively low cylinder pressure causes the fuel to atomize) ignites the fuel and again causes the fuel to burn and begin a flame front across the piston.

Detonation is the fuel actually exploding, not burning. It is igniting because of high pressure or temperature in the cylinder reaches the flash point of the fuel and this causes it to ignite from a different point than the spark plug.
 
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