Brake specific fuel consumption
Brake specific fuel consumption (BSFC) is a measure of the fuel efficiency of any prime mover that burns fuel and produces rotational, or shaft, power. It is typically used for comparing the efficiency of internal combustion engines with a shaft output.
It is the rate of fuel consumption divided by the power produced. It may also be thought of as power-specific fuel consumption, for this reason. BSFC allows the fuel efficiency of different engines to be directly compared.
- 1 The BSFC calculation (in metric units)
- 2 The relationship between BSFC numbers and efficiency
- 3 The use of BSFC numbers as operating values and as a cycle average statistic
- 4 The significance of BSFC numbers for engine design and class
- 5 Examples of values of BSFC for shaft engines
- 6 See also
- 7 References
- 8 External links
The BSFC calculation (in metric units)
To calculate BSFC, use the formula
- r is the fuel consumption rate in grams per second (g/s)
- P is the power produced in watts where
The above values of r, , and may be readily measured by instrumentation with an engine mounted in a test stand and a load applied to the running engine. The resulting units of BSFC are grams per joule (g/J)
Commonly BSFC is expressed in units of grams per kilowatt-hour (g/(kW·h)). The conversion factor is as follows:
- BSFC [g/(kW·h)] = BSFC [g/J]×(3.6×106)
The conversion between metric and imperial units is:
- BSFC [g/(kW·h)] = BSFC [lb/(hp·h)]×608.277
- BSFC [lb/(hp·h)] = BSFC [g/(kW·h)]×0.001644
The relationship between BSFC numbers and efficiency
To calculate the actual efficiency of an engine requires the energy density of the fuel being used.
Different fuels have different energy densities defined by the fuel's heating value. The lower heating value (LHV) is used for internal combustion engine efficiency calculations because the heat at temperatures below 150 °C (300 °F) cannot be put to use.
Some examples of lower heating values for vehicle fuels are:
Thus a diesel engine's efficiency = 1/(BSFC × 0.0119531) and a gasoline engine's efficiency = 1/(BSFC × 0.0122225)
The use of BSFC numbers as operating values and as a cycle average statistic
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 peak torque. The efficiency often reported for a particular engine, however, is not its maximum efficiency but a fuel economy cycle statistical average. For example, the cycle average value of BSFC for a gasoline engine is 322 g/kW·h, translating to an efficiency of 25% (1/(322 × 0.0122225) = 0.2540). Actual efficiency can be lower or higher than the engine’s average due to varying operating conditions. In the case of a production gasoline engine, the most efficient BSFC is approximately 225 g/kW·h, which is equivalent to a thermodynamic efficiency of 36%.
The significance of BSFC numbers for engine design and class
BSFC numbers change a lot for different engine design and compression ratio and power rating. Engines of different classes like diesels and gasoline engines will have very different BSFC numbers, ranging from less than 200 g/kW·h (diesel at low speed and high torque) to more than 1,000 g/kW·h (turboprop at low power level).
Examples of values of BSFC for shaft engines
The following table takes values as an example for the specific fuel consumption of several types of engines. For specific engines values can and often do differ from the table values shown below. Energy efficiency is based on a lower heating value of 42.7 MJ/kg (84.3 g/kW·h) for diesel fuel and jet fuel, 43.9 MJ/kg (82 g/kW·h) for gasoline.
|Power (kW)||Year||Engine type||Application||SFC (lb/hp·h)||SFC (g/kW·h)||Energy efficiency|
|2,050||1996||Pratt & Whitney Canada PW127 turboprop||ATR 72 regional airliner||0.477||290||29.1%|
|95||1970||Lycoming O-320 piston, gasoline||General aviation||0.460||280||29.3%|
|63||1991||GM Saturn I4 engine, gasoline||Saturn S-Series cars||0.411||250||32.5%|
|150||2011||Ford EcoBoost gasoline, turbo||Ford cars||0.403||245||33.5%|
|2,000||1945||Wright R-3350 Duplex-Cyclone gasoline, turbo-compound||Bombers, airliners||0.380||231||35.5%|
|57||2003||Toyota 1NZ-FXE, gasoline||Toyota Prius car||0.370||225||36.4%|
|550||1931||Junkers Jumo 204 two-stroke diesel, turbo||Bombers, airliners||0.347||211||40%|
|36,000||2002||Rolls-Royce Marine Trent turboshaft||Combat ships||0.340||207||40.7%|
|2,340||1949||Napier Nomad Diesel-compound||planned (aircraft intended)||0.340||207||40.7%|
|165||2000||Volkswagen 3.3 V8 TDI||Audi A8 car||0.337||205||41.1%|
|2,013||1940||Klöckner-Humboldt-Deutz DZ 710 Diesel two stroke||none (aircraft intended)||0.330||201||41.9%|
|42,428||1993||General Electric LM6000 turboshaft||Ship, electricity||0.329||200.1||42.1%|
|130||2007||BMW N47 2L turbodiesel||BMW cars||0.326||198||42.6%|
|88||1990||Audi 2.5L TDI||Audi 100 car||0.326||198||42.6%|
|3,600||MAN Diesel 6L32/44CR four-stroke||Ship, electricity||0.283||172||49%|
|34,320||1998||Wärtsilä-Sulzer RTA96-C two-stroke||Ship, electricity||0.263||160||52.7%|
|27,060||MAN Diesel S80ME-C9.4-TII two-stroke||Ship, electricity||0.254||154.5||54.6%|
Turboprops efficiency are only good at high power, for approach at low power (30% Pmax) and especially at idle (7% Pmax), SFC increases dramatically :
|Mode||Power||fuel flow||SFC||Energy efficiency|
|Nominal idle (7%)||192 hp (143 kW)||3.06 kg/min (405 lb/h)||1,282 g/kW·h (2.108 lb/hp·h)||6.6%|
|Approach (30%)||825 hp (615 kW)||5.15 kg/min (681 lb/h)||502 g/kW·h (0.825 lb/hp·h)||16.8%|
|Max cruise (78%)||2,132 hp (1,590 kW)||8.28 kg/min (1,095 lb/h)||312 g/kW·h (0.513 lb/hp·h)||27%|
|Max climb (80%)||2,192 hp (1,635 kW)||8.38 kg/min (1,108 lb/h)||308 g/kW·h (0.506 lb/hp·h)||27.4%|
|Max contin. (90%)||2,475 hp (1,846 kW)||9.22 kg/min (1,220 lb/h)||300 g/kW·h (0.493 lb/hp·h)||28.1%|
|Take-off (100%)||2,750 hp (2,050 kW)||9.9 kg/min (1,310 lb/h)||290 g/kW·h (0.477 lb/hp·h)||29.1%|
- Fuel economy in automobiles
- Fuel economy-maximizing behaviors
- Fuel management systems
- Marine fuel management
- Thrust specific fuel consumption
- "ATR: The Optimum Choice for a Friendly Environment" (PDF). Avions de Transport Regional. June 2001. p. PW127F engine gaseous emissions.
- Michael Soroka (March 26, 2014). "Are Airplane Engines Inefficient?".
- "Advanced Gasoline Turbocharged Direct Injection (GTDI) Engine Development" (PDF). Ford Research and Advanced Engineering. May 13, 2011.
- Kimble D. McCutcheon (27 October 2014). "Wright R-3350 "Cyclone 18"" (PDF).
- "Development of New-Generation Hybrid System THS II - Drastic Improvement of Power Performance and Fuel Economy". Society of Automotive Engineers. 8 March 2004.
- inter-action association, 1987
- "Marine Trent". Civil Engineering Handbook. 19 Mar 2015.
- "Napier Nomad". Flight. 30 April 1954.
- "The new Audi A8 3.3 TDI quattro: Top TDI for the luxury class" (Press release). Audi AG. July 10, 2000.
- "Jane's Fighting Aircraft of World War II". Bracken Books. 1989.
- "LM6000 Marine Gas Turbine" (PDF). General Electric. 2016.
- "BMW 2.0d (N47)" (in French). Auto-innovations. June 2007.
- "The New Audi 5-Cylinder Turbo Diesel Engine: The First Passenger Car Diesel Engine with Second Generation Direct Injection". Society of Automotive Engineers. 1 February 1990.
- "Four-Stroke Propulsion Engines" (PDF). Man Diesel. 2015.
- "RTA-C Technology Review" (PDF). Wärtsilä. 2004. Archived from the original on December 26, 2005.
- "MAN B&W S80ME-C9.4-TII Project Guide" (PDF). Man Diesel. May 2014.
- Reciprocating engine types
- HowStuffWorks: How Car Engines Work
- Reciprocating Engines at infoplease
- Piston Engines US Centennial of Flight Commission
- Effect of EGR on the exhaust gas temperature and exhaust opacity in compression ignition engines
- Heywood J B 1988 Pollutant formation and control. Internal combustion engine fundamentals Int. edn (New York: Mc-Graw Hill) pp 572–577
- Well-to-Wheel Studies, Heating Values, and the Energy Conservation Principle