Calculate engine thermal efficiency from fuel consumption data using SAE J1349 standard conditions and Otto cycle analysis.
Input Parameters
Results
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Brake Thermal Eff
%
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Ideal Otto Eff
%
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Fuel Flow
kg/hr
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Heat Rejected
kW
Note: Modern gasoline engines achieve 35-40% brake thermal efficiency. The Otto cycle sets the theoretical maximum. SAE J1349 corrects to standard atmospheric conditions (25°C, 100 kPa).
Reference
Brake kW = BHP × 0.7457
Fuel Flow = BSFC × Power (kW) / 1000
Fuel Energy = Fuel_flow × LHV / 3.6
Brake Eff = Power / Fuel_energy × 100
Otto Eff = 1 − 1/CR^(gamma−1), gamma=1.35