You know, I never fully understood the term "H.P. / Hr.".
I can understand "lbs./hr.", in the fuel consumption rating, but ".../H.P. / Hr."?
Can someone please explain?
It's brake specific fuel consumption (BSFC).
The BSFC measures the thermal efficiency of the engine.
Efficiency can be calculated as the ratio of the power generated to the potential power in the fuel. That is, if you have 30kW generated and the fuel youuse has a potential power of 100kW, your efficiency is 30%.
lb (fuel)/hour is a different way of expressing the fuel power. HP is the power generated.
Let's take the figure of 0.5lb/hp/hr.
The fuel flow rate is 0.5lb/hr per hp
Convert that to metric (cos it's easier) the fuel flow rate is 0.2268kg/hr or 0.000063kg/s.
The energy content of petrol is approximately 45MJ/kg
Multiplying the energy content and fuel flow rate gives the potential power in the fuel.
0.000063kg/s × 45MJ/kg = 2.835kJ/s = 2.835kW
The output is 1hp = 0.7457kW.
The efficiency is 0.7457kW/2.835kW = 26.3%
BSFC of 0.53lb/hp/hr = 24.8%