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240racer · 12-10-2002, 03:01 PM

I think the main thing that you guys are trying to get at is Brake Specific Fuel Comsumption.  Usually just bsfc, it says how many gallons of fuel per hour are used to make a certain amount of brake horsepower for an hour.  It's funny, most engines are pretty close to the same in this respect.  Turbo engines actually tend to be higher, since they tend to run richer at peak power.  However, the turbo engine that makes the same power as a non-turbo engine probably has a better BSFC at lets say half or full power, which is more relelvent to cruising anyway.
The other thing to look at is the power to weight of the engine itself.  This is important for racing, airplanes and fuel economy.  Remember it takes less power to accelerate less weight at the same rate.  Airplanes have gone to gas turbine engines now because they are vastly superior in power to weight.  One aspect of weight is just the size of the engine itself, Volume wise.  Since most engines are made out of similar density materials, the smaller it is, the lighter it is.  If you can make more power per displacement (specific HP) then you are more efficient.
As far as diesel engines go, the fuel itself has more energy per lb then gasoline, that's a big reason why it has higher efficiency.  The other reason is that they aren't worried about the weight of the engine, just it's BSFC, so everything is tailored toward that.  The main drawback of diesel engines is they are not able to run at high RPMs due to the difficulty of getting all the necessary fuel in at the correct time.  The current high-tech diesels use direct fuel injection and they use the timing of the fuel to control the timing of the combustion since they don't have spark plugs.  The cylinder pressures are very high when the piston is at TDC (if the C/R is 15:1, which is low, then the pressure is 220psi absolute) The fuel pressure has to be considerably higher then that for the fuel to even flow into the cylinder.  Fuel pressures of over 1000psi are not uncommon.  As they are able to reliably increase fuel pressure, they will be able to increase RPM, and then make more power.
BSFC examples can be found on the web
here are a couple examples:

0.26-0.34 Large industrial four-stroke diesel engines (very small hp/weight ratios)

0.28-0.36 Other four-stroke diesel engines

0.32-0.38 Two-stroke diesel engines

0.37-0.44 Fuel injected four-stroke gasoline aircraft engines

0.40-0.48 Fuel injected four-stroke gasoline automobile engines

0.43-0.48 Carburetted four-stroke gasoline aircraft engines

0.48-0.60 Carburetted four-stroke automobile engines

0.55+ Two stroke gasoline engines

0.55-0.70 Four-stroke aircraft engine takeoff fuel flows

the units are lbs/hr/HP

12-10-2002, 03:01 PM	#9
240racer Zilvia Junkie Join Date: Nov 2001 Location: Minneapolis, MN Age: 42 Posts: 574 Trader Rating: (0)	I think the main thing that you guys are trying to get at is Brake Specific Fuel Comsumption.  Usually just bsfc, it says how many gallons of fuel per hour are used to make a certain amount of brake horsepower for an hour.  It's funny, most engines are pretty close to the same in this respect.  Turbo engines actually tend to be higher, since they tend to run richer at peak power.  However, the turbo engine that makes the same power as a non-turbo engine probably has a better BSFC at lets say half or full power, which is more relelvent to cruising anyway. The other thing to look at is the power to weight of the engine itself.  This is important for racing, airplanes and fuel economy.  Remember it takes less power to accelerate less weight at the same rate.  Airplanes have gone to gas turbine engines now because they are vastly superior in power to weight.  One aspect of weight is just the size of the engine itself, Volume wise.  Since most engines are made out of similar density materials, the smaller it is, the lighter it is.  If you can make more power per displacement (specific HP) then you are more efficient. As far as diesel engines go, the fuel itself has more energy per lb then gasoline, that's a big reason why it has higher efficiency.  The other reason is that they aren't worried about the weight of the engine, just it's BSFC, so everything is tailored toward that.  The main drawback of diesel engines is they are not able to run at high RPMs due to the difficulty of getting all the necessary fuel in at the correct time.  The current high-tech diesels use direct fuel injection and they use the timing of the fuel to control the timing of the combustion since they don't have spark plugs.  The cylinder pressures are very high when the piston is at TDC (if the C/R is 15:1, which is low, then the pressure is 220psi absolute) The fuel pressure has to be considerably higher then that for the fuel to even flow into the cylinder.  Fuel pressures of over 1000psi are not uncommon.  As they are able to reliably increase fuel pressure, they will be able to increase RPM, and then make more power. BSFC examples can be found on the web here are a couple examples: 0.26-0.34 Large industrial four-stroke diesel engines (very small hp/weight ratios) 0.28-0.36 Other four-stroke diesel engines 0.32-0.38 Two-stroke diesel engines 0.37-0.44 Fuel injected four-stroke gasoline aircraft engines 0.40-0.48 Fuel injected four-stroke gasoline automobile engines 0.43-0.48 Carburetted four-stroke gasoline aircraft engines 0.48-0.60 Carburetted four-stroke automobile engines 0.55+ Two stroke gasoline engines 0.55-0.70 Four-stroke aircraft engine takeoff fuel flows the units are lbs/hr/HP __________________ Adam '89 coupe KA24DE+T 14.1 @ 104 MPH '88 Celica All-Trac turbo stock, but no more ecu codes!!