Brake specific fuel consumption

As far as I am aware there is only SFC (Specific Fuel Consumption)

This is measured in kg,g, or litres/kWh. (If given in g or kg, you will need to know the SG of the fuel to convert it into litres). You can then calculate your hourly consumption rates under varying conditions of load and/or speed.

These figures are usually shown in graphical form in the workshop manual.

The common terms with brake in them, are brake power and brake mean effective pressure.

BSFC is probably more common, although both are used. "Brake" simply means that the fuel consumption is as actually measured on a dynamometer (brake). The Wikipedia article uses the terms interchangeably. "Indicated" SFC would not take into account frictional losses (but would only shoe up in a theoretical sense). The term "indicated" also shows up with "effective pressure." This article, near the end, describes the differences in the terms. Here, the distinction make a little more sense, because one would come from integrating actual measured cylinder pressures, the other from figuring out what they must be based on engine output.

Usually BSFC is not "calculated", but rather measured (thus the brake part). I'm guessing that the original poster may be more interested in how this figure is used in calculations. As you said, the BSFC tells you how much fuel is used per kWh of engine output. A typical value would be 300g/kWh, so a 100 kW engine, running for one hour, would use 30,000 grams or 30 kg in one hour. If this engine were on a vehicle and you knew the speed of the vehicle when the engine is producing 100kW, then you could calculate miles per gallon or liters per hundred km.

Hi Ken,

"Indicated" SFC would not take into account frictional losses (but would only shoe up in a theoretical sense).

Therefore when speaking about SFC and looking at SFC graphs it always is related to an actual figure of fuel consumption..............because really there is no such animal as "Indicated" SFC. and as I said I certainly have never heard anything used but SFC. However that does not mean the term does not exist. It is just something that I have never used.

I agree that certainly use the term MEP which is used when calculating IP, developed in any particular cylinder of an engine............usually only ever done on medium and low speed engines.

There is also TSFC (thrust specific fuel consumption). There should also be NSFC which relates to how much fuel is used by teenagers to make exhaust noise... and the closely related MSCF (Music Specific Fuel Consumption) which has to do with the fuel consumed in running huge stereos in cars.

Our original poster may find this chart enlightening. It shows, among other things, that the BSFC of a VW TDI (which is where this map comes from) is as low as 197 g/kWh, which represents 40% efficiency, provided one can keep the engine chugging along at low speed. At the 20 hp line, you can see that by running the engine in too low a gear, (high rpm) the specific fuel consumption can more than double.

On IO-550 piston aircraft engines the fuel consumption should be 0.6 #/hp-h. So if you have a 300 hp engine: 300hp * 0.6#/hp-h * g/5.8# = 31 g/h at sea level. Hope this helps.