BSFC Numbers for Rotary

[NoDOHC]

Originally Posted by vex

Fix some of your issues with your math

The math is correct as far as I can tell. I used an intermediate density of 0.72g/mL because gasoline covers a broad range of densities. Perhaps you don't like that I used engineering units. (I really didn't want to put 0.0001656 L/rev).

Originally Posted by ReTed

You might be right about a steady state snap shot of the engine, but when most people describe "BSFC" for a particular engine, we're talking about the average BSFC for all ranges.

I've heard 0.60 - 0.65 used in most applications when talking about a 13B.

Actually BSFC is typically expressed as a chart with engine load on one axis, speed on the other axis and BSFC indicated by islands (similar to a compressor isentropic efficiency map for a turbo).

Many engines are rated at peak BSFC which is commonly computed at the highest BMEP (highest torque output). This is the point that I picked.

I will develop a full load BMEP curve for my engine at a variety of speeds, but not tonight. I don't have partial load data.

I agree that you have heard those numbers, so have I, but I also heard that I should never exceed 26 degrees of ignition advance and to always run rich of 12:1 AFR. If you do that, you will have a BSFC of 0.6 lb/HPh

[RETed]

Originally Posted by NoDOHC

Actually BSFC is typically expressed as a chart with engine load on one axis, speed on the other axis and BSFC indicated by islands (similar to a compressor isentropic efficiency map for a turbo).

Many engines are rated at peak BSFC which is commonly computed at the highest BMEP (highest torque output). This is the point that I picked.

I realize that engineer-types would insist on a graph version, but most laymen would just see a single number.

I have to disagree that this single number is highest BMEP...

Any engine will have different BSFC values at different speeds and loads. For example, a reciprocating engine achieves maximum efficiency when the intake air is unthrottled and the engine is running near its torque peak. However, the numbers often reported for a particular engine are a fuel economy cycle average statistic.

Taken from: http://en.wikipedia.org/wiki/Brake_s...el_consumption


-Ted