Brake Specific Fuel Consumption

What is Brake Specific Fuel Consumption?

Brake Specific Fuel Consumption (BSFC) is a measure of an engine's efficiency. It tells you how much fuel an engine consumes to produce a given amount of power. A lower BSFC value means the engine is more efficient it can produce the same power while burning less fuel. BSFC is widely used by engineers and automotive enthusiasts to compare engine performance across different sizes and types.

BSFC is measured in grams per kilowatt-hour (g/kWh) in metric units or pounds per horsepower-hour (lb/hp·h) in imperial units. Unlike simple fuel consumption which only tells you how much fuel an engine uses BSFC accounts for the power output giving you a true picture of efficiency.

How to Calculate BSFC

The formula for Brake Specific Fuel Consumption is straightforward:

$$BSFC = \frac{r}{P}$$

Where:

• $r$ is the fuel consumption rate (in g/s or lb/h)
• $P$ is the engine power output (in kW or hp)

To convert from torque and RPM to power you can use these formulas:

• Metric: $P(kW) = \frac{\tau(Nm) \times \omega(RPM)}{9549}$
• Imperial: $P(hp) = \frac{\tau(lb\cdot ft) \times \omega(RPM)}{5252}$

Once you have the BSFC value you can calculate the engine's thermal efficiency by considering the energy density of the fuel being used.

How to Calculate Engine Efficiency from BSFC

To find the thermal efficiency of an engine from BSFC:

$$\eta = \frac{1}{e_d \times BSFC} \times 100\%$$

Where $e_d$ is the energy density of the fuel in kWh/g. Different fuels have different energy densities:

• Methane: 0.0139 kWh/g
• LPG: 0.01264 kWh/g
• Gasoline: 0.01206 kWh/g
• Diesel fuel: 0.01183 kWh/g
• Kerosene: 0.01194 kWh/g

How to Use This BSFC Calculator

Using this BSFC calculator is simple. Start by selecting your preferred unit system Metric (g/s kW) or Imperial (lb/h hp). Choose your input mode you can enter power directly or provide torque and RPM values and the calculator will compute the power for you. Enter the fuel consumption and the power (or torque and RPM). Select the fuel type to get the engine efficiency estimate. The results will update instantly showing the BSFC value engine efficiency and hourly fuel consumption.

This tool is ideal for automotive engineers mechanics students and anyone interested in understanding engine performance and efficiency.