combustion efficiency

[woollymoof]

Hi all,

Does anyone out there know how to measure or calculate combustion efficiency?

[woollymoof]

Hi all,

Does anyone out there know how to measure or calculate combustion efficiency?

[BryanH]

Wooly, you can measure combustion efficiency by logging mass air flow, fuel flow and bhp during a dyno run and calculating BSFC. (do a search)
Extremes of BSFC are Hotrodded sidevalve ford v8 at .68 to Honda F1 turbo at .35
Interesting diagnostic tool. Superflow dyno has realtime BSFC readout. I calc first try fuel maps using est. BSFC, injector flow rates and est. bhp.
You can calc BSFC if you have injector flow rate, s.g.of fuel and inj duty cycle at peak power. Its lbs per bhp per hour

" BG Engineering Consultant Chuck Jenckes says it's critical to use A/F ratio as a tuning guide, not brake-specific fuel consumption (BSFC) numbers. BSFC is something that's logged on every good dynamometer. It's a measure of the engine's efficiency, expressed in units of {(mass of fuel)/power}. Analyzing the BSFC trend across a dyno pull can highlight rich or lean operating points, but Jenckes advises not to tune to a specific BSFC value. Why? Because BSFC is sensitive to every part of the engine combination, so it's not a relative basis for comparison. For example, if we'd replaced our electric-drive water pump with an engine-driven pump, losing an average of 4 hp to friction, our BSFC values would increase even though we didn't actually change the basic combination. A/F ratio is a more precise tuning standard."

[Chris Davin]

To me, "combustion efficiency" means the ratio of how much energy is released in combustion to the stored chemical energy in the fuel. Under this definition, combustion efficiencies of modern engines are very high - greater than 95% at A/F ratios close to stoichiometric. You can calculate the combustion efficiency of your motor by using an exhaust gas sniffer to measure the concentrations of hydrocarbons, NOx, and carbon monoxide in the exhaust. Knowing the energy stored in these components, you can then calculate how much power is lost to incomplete combustion.

But since combustion losses are typically very small, they are not usually a concern. As someone else pointed out, you're probably more concerned with brake-specific fuel consumption (BSFC), which has already been discussed.

[Bam Bam]

Yeah
combustion efficiency

Energy out/Energy in

ie.
Power/(fuel flow * lower heating value)

as Halfast said doesn't tell you alot.

in a restricted environment maximizing horsepower per unti air flow would be better. Unless your

[woollymoof]

Bam Bam,
Wouldn't that be thermal efficiency?

I assumed that combustion efficiency would be

(shaft power + power lost from radiators and cooling + power lost through exhaust (in heat))/(fuel flow * lower heating value)

i.e. what chris said.

The reason I'm interested in combustion efficiency is "according to my calculations" small changes in combustion efficiency, or thermal efficiency, create large power gains.

[John Bucknell]

Combustion efficiency is percent fuel converted to heat.

Thermal efficiency is percent of heating value of fuel converted to work (indicated or net).

Mechanical efficiency is percent of thermally created work actually usable.

Lots of other ways to cut it.