Thread: Constant Volume Combustion Engine (6-Stroke Engine)

Originally Posted by jboy

Read it more closely.......

"The correct technical definition of this new type of engine is: 6-stroke isovolumetric engine with revolving con-rod and half-floating piston."

Here is how I see it and "what they call it"

Intake stroke "Intake"
Pause/intake completion, the intake velocity will force alittle more in
Compression stroke "Compression"
pause/Ignition "Constant Volume Combustion"
Power stroke "Full expansion stroke"
pause/exhaust pressure release "Free exhaust"
exhaust stroke "Forced exhaust"
pause/exhaust clear, intake begin with extended scavenging

this all still happens in 720º of crankshaft rotation, ? 4 strokes ?

it still only has 4 strokes with a pause at TDC and BDC
I don't think these pauses should be called strokes......
Mabe a 6 cycle engine

but it has realy has 8 stages.....

This looks like a good idea but it termed wrong

also this seemes like a good setup for a super charger where the top and bottom intake pauses could allow alot of air/fuel to be stuffed into the cylinder.........

lets see what others have to say before I go on

Yeah, i agree that the terminology is a bit skewed. after all, the cylinder is must only travel up and down twice per combustion sequence.

if this engine was running in a forced induction, i would be worried that without proper downtuning of the turbo/super charger, you would run the risk of over feeding the engine. also, the problem of detination would further increased due to the momentary pause at the top of the compression cycle. normally aspirated engines run the timing such that the igntion spark occurs slightly before TDC on the compression stroke. when you add forced induction, be it turbo or supercharger, you have to retard the timing so that you dont detonate the mixture in the split second before complete compression occurs. this means that the ignition would have to occur before TDC... negating a huge purpose of this engine... ignition AFTER the piston has stopped at TDC.

now, from just a "get the most fuel in a possible" position. yes, i think that a turbo or super charger would be nice on this engine, given the fact that the entire cylinder would be able to be pressurized to the full boost ammount of the FI equipment.

however, you would have to take a look at the overall effect of adding boost to an engine like this. what are the tradeoffs, and how much does the added performance detract from the gains in technology.

Anyone with other thoughts... prove me wrong... anything.
~Mike

I don't think that you would ever have to set timing after TDC if you did I think that you would have the wrong combo. Worst case IMHO would be at TDC. Part of the idea is to optimize the piston speed to the dynamics of the ports etc. I'd thing that it would be significantly different for supercharged engines (less need to suck in charge) and significantly different again for Turbos (have to push the exhaust out)
All IMHO. Please feel free to prove me wrong.

Hm, just to nit pick. Rotary engines do in fact have pistons. Technically, the part that most people refer to as the "rotor" should be called a piston regardless of the characteristics of it's motion.

Sometime way back in the 70's caddies had electric shut off valves in the intake. It would drop back to 6 cyl, then to 4cly when the time war right.

Originally Posted by Aaron Cake

Hm, just to nit pick. Rotary engines do in fact have pistons. Technically, the part that most people refer to as the "rotor" should be called a piston regardless of the characteristics of it's motion.

good point!

~mike

Forgive me if I sound stupid, but I always thought that ignition occurs before TDC because it takes that long for expansion to build. Detonation is caused by too much expansion before TDC, thus shoving the cylinder down before the crank lets it.
The article says that energy is lost by combustion occuring before TDC, putting backpressure on the crank. I don't think this is true, any thoughts?

Originally Posted by PatO

Forgive me if I sound stupid, but I always thought that ignition occurs before TDC because it takes that long for expansion to build. Detonation is caused by too much expansion before TDC, thus shoving the cylinder down before the crank lets it.
The article says that energy is lost by combustion occuring before TDC, putting backpressure on the crank. I don't think this is true, any thoughts?

As I remember (since I haven't read the article since this was a new thread ) the main advantage that this engine has is the ability to optimize the up and down movement of the pistons. Because of this ability, the piston can stay at TDC for as long as the engine designer wants it to. Therefore, the pressure in the cylinder can be building (while the piston is basically paused at TDC for several degrees of crank rotation) without putting any backwards force on the crank shaft. In a conventional engine, the piston spends very little time at TDC, so like you said, it needs the extra burning time before TDC to get the cylinder pressure up before the trip down. The result of firing before TDC is that the cylinder pressure is higher on the power stroke. The building back pressure before TDC is a necessary evil with a conventional crank, but with this other type of engine, you get your high pressure during the power stroke without the back pressure on the crank shaft before TDC. Any clearer?

Originally Posted by PatO

Forgive me if I sound stupid, but I always thought that ignition occurs before TDC because it takes that long for expansion to build. Detonation is caused by too much expansion before TDC, thus shoving the cylinder down before the crank lets it.
The article says that energy is lost by combustion occuring before TDC, putting backpressure on the crank. I don't think this is true, any thoughts?

the reason that energy is lost with ignition before TDC is that when the mixture ignites, the piston is still traveling upward to TDC. this means that some of the energy produced in the explosion of the air/fuel mixture is actually pressing against the piston, effecticly fighting against the motion of the piston. once the piston reaches TDC, then the energy of the expanding gasses presses the piston downward... a good use of the energy

in the ducati engine, the piston arrives at TDC, before the ignition starts. this means the mixture is allowed to compress, and then ignite when the volume of the combustion chamber is not changing...no combution forces acting AGAINST the piston. as it ignites, the pressure builds and after a given time... the piston is allowed to move downward due to the pressure in the chamber. this means that more of the energy is used to push the piston downward after TDC.

granted, you still have some energy loss to heat, but that is another topic...

~Mike

Originally Posted by Aaron Cake

Hm, just to nit pick. Rotary engines do in fact have pistons. Technically, the part that most people refer to as the "rotor" should be called a piston regardless of the characteristics of it's motion.

Damn, now I have to change my username.