Brake specific fuel consumption
Encyclopedia
Brake Specific Fuel Consumption (BSFC) is a measure of fuel efficiency
within a shaft reciprocating engine
.
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 reciprocating engines to be directly compared.
Where:
The resulting units of BSFC are gram
s per joule
(g·J−1)
Commonly BSFC is expressed in units of grams per kilowatt-hour (g/(kW·h)). The conversion factor is as follows:
The conversion between metric and imperial units is:
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 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)
cycle average statistic. For example, the cycle average value of BSFC for a gasoline engine is 322 g/(kW·h), translating to an efficiency of 25%. However, efficiency for that engine can be lower or higher than this average statistic depending on the operating condition. 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%.
A fuel island plot of a diesel engine BSFC is shown. The sweet spot at 206 BSFC has 40.6% efficiency.
(C8H18) (based on change in Gibbs free energy
going to gaseous H2O and CO2) is 45.7 MJ/kg, corresponding to 79 g/(kW·h).
Fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...
within a shaft reciprocating engine
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...
.
It is the rate of fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
consumption divided by the power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
produced. It may also be thought of as power-specific
Specific
Specific may refer to:* Specificity* Specific, a cure or therapy for a specific illnessLaw:* Specific deterrence, focussed on an individual* Specific finding, intermediate verdict used by a jury in determining the final verdict...
fuel consumption, for this reason. BSFC allows the fuel efficiency of different reciprocating engines to be directly compared.
The BSFC calculation (in metric units)
To calculate this rate, use the formula Where:
- r is the fuel consumption rate in grams per second (g·s-1)
- P is the power produced in watts where
is the engine speed in radians per second (rad·s-1)
is the engine torque in newton meters (N·m)
The resulting units of BSFC are gram
Gram
The gram is a metric system unit of mass....
s per joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
(g·J−1)
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 cannot be put to use.
Some examples of lower heating values for vehicle fuels are:
-
- Certification gasolineGasolineGasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
= 18,640 BTUBritish thermal unitThe British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...
/lb (0.01204 kW·h/g) - Regular gasoline = 18,917 BTU/lb (0.0122225 kW·h/g)
- Diesel fuel = 18,500 BTU/lb (0.0119531 kW·h/g)
- Certification gasoline
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 torque peak. However, the numbers often reported for a particular engine are a fuel economyFuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
cycle average statistic. For example, the cycle average value of BSFC for a gasoline engine is 322 g/(kW·h), translating to an efficiency of 25%. However, efficiency for that engine can be lower or higher than this average statistic depending on the operating condition. 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%.
A fuel island plot of a diesel engine BSFC is shown. The sweet spot at 206 BSFC has 40.6% efficiency.
The significance of BSFC numbers for engine design and class
The beauty of BSFC numbers is that they remain similar over a wide range of engine sizes. These numbers only change for different engine designs and compression ratios. For example, a small one cylinder 50 cc four-stroke and a large V8 engine can both have the same BSFC number. However, engines of different classes like diesels and gasoline engines will have very different BSFC numbers.Typical values of BSFC for shaft engines
The following table gives the minimum specific fuel consumption of several types of engine. For comparison, the theoretical work that can be derived from burning octaneOctane
Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH36CH3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain...
(C8H18) (based on change in Gibbs free energy
Gibbs free energy
In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure...
going to gaseous H2O and CO2) is 45.7 MJ/kg, corresponding to 79 g/(kW·h).
| Power | year | Engine type | Application | SFC in lb/(hp·h) | SFC in g/(kW·h) | Energy efficiency Energy conversion efficiency Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:... |
|---|---|---|---|---|---|---|
| Turbo-prop | 0.8 | 360 to 490 | 17 to 23% | |||
| Otto cycle Otto cycle An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines.... gasoline engines |
.45 to .37 | 273 to 227 | 30 to 36% | |||
| Diesel engine Diesel engine A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber... turbocharged diesels |
.34 to .30 | 209 to 178 | 40 to 47% | |||
| 2000 kW | 1945 | Wright R-3350 Duplex-Cyclone gasoline turbo-compound | aircraft engine | 0.4 | 243 | 33.7% |
| 57 kW | Toyota Prius Toyota Prius The Toyota Prius is a full hybrid electric mid-size hatchback, formerly a compact sedan developed and manufactured by the Toyota Motor Corporation... THS II engine only |
automobile | 225 | 37% | ||
| 68 kW | 2008 | Revetec Controlled Combustion Engine Controlled Combustion Engine Controlled Combustion Engine is a term used by Revetec, an engine design company, to identify a type of experimental internal combustion engine designed by Brad Howell-Smith. It uses two counter-rotating cams instead of a crankshaft... gasoline engine |
automobile | 212 | 38.6% | |
| 550 kW | 1931 | Junkers Jumo 204 Junkers Jumo 204 -Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*... turbocharged two-stroke diesel |
aircraft engine | 210 | 39.8% | |
| 36 MW | 2002 | Rolls-Royce Marine Trent Rolls-Royce Marine Trent -References:* Rolls-Royce plc Press release.-External links:*... turboshaft Turboshaft A turboshaft engine is a form of gas turbine which is optimized to produce free turbine shaft power, rather than jet thrust... |
marine engine | 210 | 39.8% | |
| 2340 kW | 1949 | Napier Nomad Napier Nomad The Napier Nomad was a complex British compression-ignition aircraft engine designed and built by Napier & Son in 1949. Two versions were flight tested:... Diesel-compound |
aircraft engine | 0.345 | 210 | 39.8% |
| 165 kW | 2000 | Volkswagen Volkswagen Volkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is... 3.3 V8 TDI |
automobile engine | 0.33 | 205 | 41.1% |
| 43 MW | General Electric LM6000 General Electric LM6000 -External links:*... turboshaft Turboshaft A turboshaft engine is a form of gas turbine which is optimized to produce free turbine shaft power, rather than jet thrust... |
marine engine, power generation | 42% | |||
| 88 kW | 1990 | Audi 2.5 litre TDI | automobile engine | 198 | 42.5% | |
| 213 kW | Volvo Volvo AB Volvo is a Swedish builder of commercial vehicles, including trucks, buses and construction equipment. Volvo also supplies marine and industrial drive systems, aerospace components and financial services... D7E 290 hp diesel |
truck engine | 188 | 44.8% | ||
| 80 MW | 1998 | Wärtsilä-Sulzer RTA96-C Wärtsilä-Sulzer RTA96-C The Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä. It is currently considered the largest reciprocating engine in the world, designed for large container ships, running on heavy fuel oil... two-stroke |
marine engine | 163 | 51.7% | |
| 23 MW | MAN Diesel S80ME-C Mk7 two-stroke | marine engine | 155 | 54.4% |
See also
- Fuel economy in automobilesFuel economy in automobilesFuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
- Fuel management systemsFuel management systemsFuel management systems are used to maintain, control and monitor fuel consumption and stock in any type of industry that uses transport, including rail, road, water and air, as a means of business....
- Marine fuel managementMarine fuel managementMarine fuel management is a multi-level approach to measuring, monitoring, and reporting fuel usage on a boat or ship, with the goals of reducing fuel usage, increasing operational efficiency, and improving fleet management oversight...
- Thrust specific fuel consumption