hjholter3

power / (total fuel mass input - unprocessed fuel input* )

*present in exhaust from Combustion chamber

higher numbers win.

stilettoman

iTrader: (1)

Ignoring the unburned fuel does not make much sense to me when you are trying to measure efficiency.

Since the 1930s, maybe before that, the efficiency of internal combustion engines has been measured by what has always been called Specific Fuel Consumption(SFC). This is simply pounds of fuel consumed per horsepower per hour. You can change the units to metric or whatever, but it still means the same thing. Piston aircraft engines were getting SFC of about 0.5 pounds per horsepower-hour in the late 1930s, and I think the best gasoline engines of today are getting about 0.45. Of course this is easy with an airplane engine. An automobile engine spends very little time at any optimum power setting.

This is not to be confused with Specific Output, which is power produced per unit of displacement, as horsepower per cubic inch, kilowatts per liter, or whatever. The turbos are the best here, of course.

Mazda's researchers about 10 years ago developed a research engine with a lot of ceramic and light weight parts, and were bragging that they got within 10% of the specific fuel consumption of the best piston engines. This would certainly have referred to gasoline fueled engines - they would never have gotten within 10% of a modern Diesel.

hjholter3

I prefer the CCE measurement.

if you're spitting fuel out the exhaust, that isn't an efficent combustion chamber, now is it?

stilettoman

iTrader: (1)

"if you're spitting fuel out the exhaust, that isn't an efficent combustion chamber, now is it?"

If you are spitting fuel out the exhaust that is certainly inefficient combustion. It would most likely be caused by overly rich carb or fuel injection, but could be caused by poor ignition, bad cam timing or port timing, screwed up emissions equipment, or even a poorly designed combustion chamber.

hjholter3

Given that all other factors have been ruled out, why do rotary engines have fuel exiting via the exhaust, rather than being fully combined with oxidizer and combusted?

digitalsolo

iTrader: (2)

Because the "squish" zones in a rotary suck. Fuel can be pushed to the edges of the chamber far from spark and remain unburned during the combustion process, which kills emissions and is the primary reason for their crappy torque, and weak power per liter (a ~140 hp 2.6L engine isn't all that great, Honda whoops on that with Civics...)

This can occur in piston engines as well, especially when you start bringing up the bore size, but with proper piston and combustion chamber design the area in the combustion chamber where this occurs can be designed to induce compression firing of the fuel. I'm sorry that I'm not explaining this to well, but it's why you'll see pistons that are mostly flat with raised areas off to one side, the raised area is to increase the "squish" and help fire off more of the fuel. This gets really exaggerated in engines like the Hemi, where the combustion chamber design sucks for CCE.

hjholter3

Dude, I understood what you were saying

No matter how you do it, you're going to get a less efficient combustion chamber with the rotary design, which as you said impairs torque creation and makes the engine seem so fuel inefficent.

That is what is so damning about the rotary concept...

Because a piston engine can displace so many cubic inchs whilst being only so large, so heavy and yet remain efficient and actually produce more power, whilst a rotary becomes huge and more theoretically inefficient due to its design.