Engine Power from Fuel

The brake power output is derived from fuel energy input multiplied by thermal efficiency:

• ṁ_f — fuel mass flow rate (kg/s)
• CV — calorific value of fuel (kJ/kg)
• η — brake thermal efficiency (decimal)

BSFC — Brake Specific Fuel Consumption

BSFC indicates how efficiently the engine converts fuel to work. Lower is better. Typical diesel: 190–230 g/kWh.

BMEP — Brake Mean Effective Pressure

• n_R — revolutions per power stroke (2 for 4-stroke, 1 for 2-stroke)
• V_d — total displacement (m³)
• n — engine speed (rev/s)

Torque

ISO 3046 Power Rating Types

Rating	Code	Factor	Description
Continuous	COP	1.0×	Unlimited hours at constant load
Prime	PRP	1.1×	Unlimited hours, variable load, avg ≤ 80% of PRP
Limited Time	LTP	1.2×	Max 500 h/year at 100% LTP
Emergency Standby	ESP	1.3×	Max 200 h/year, no overload allowed

Practical Example

Diesel vs Gas Engine Comparison

Parameter	Diesel	Natural Gas
Thermal Efficiency	35–52%	28–42%
BSFC (equivalent)	190–230 g/kWh	230–300 g/kWh
BMEP (turbocharged)	15–25 bar	12–20 bar
A/F Ratio (stoich.)	14.5:1	17.2:1
Compression Ratio	15–22:1	10–14:1
CO₂ per kWh	~650 g	~490 g
NOx	Higher	Lower (lean burn)

Typical Engine BSFC Values

Engine Type	BSFC (g/kWh)	Efficiency
Small high-speed diesel (<100 kW)	230–270	30–36%
Medium-speed diesel (100–1000 kW)	195–230	35–42%
Large medium-speed (1–10 MW)	180–200	40–46%
Slow-speed marine diesel (10+ MW)	160–175	48–52%
Gas engine (lean burn)	230–280 (eq.)	35–42%