Specific fuel consumption

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The specific fuel consumption is a measure of the efficiency of an internal combustion engine . It is defined as the ratio between fuel consumption per period and the mechanical power output. There is a comparable characteristic value for jet and rocket engines. It is described in the article Specific Impulse .

The specific fuel consumption is usually given in g / kWh .

Specific fuel consumption as a benchmark

Internal combustion engines can only be compared with one another on the basis of the specific fuel consumption if the power measurement is carried out according to the same standards and the fuels have the same calorific value per unit weight. The article horse power shows which different measurement methods are used to determine engine power.

Conversion into other units

In the Anglo-American system of measurement , the specific fuel consumption of internal combustion engines that deliver the power to a shaft is called Brake Specific Fuel Consumption (abbr .: BSFC) and is specified in lb / (hp · h). Older German-language literature also gives fuel consumption in grams per horsepower hour (g / PSh).

Conversion table
lb / (hph) g / kWh g / PSh
1 g / kWh = 0.001644 - 0.73549875
1 lb / (hp * h) = - 608.277 447,387258
1 g / PSh = 0.0022352 1.3596216 -

In Anglo-American, the decimal point is to be replaced by a decimal point.

Specific fuel consumption and efficiency

Relationship between specific fuel consumption (b e ) of a gasoline or diesel engine and efficiency η at a given calorific value (H U )

The efficiency of an internal combustion engine relates to the calorific value of the fuel and not to its (higher) calorific value . The calorific value is usually given in kJ / kg or kWh / kg. The conversion is: 1 kWh = 3600 kJ. If the specific fuel consumption (b e ) and calorific value (H U ) of the fuel are known, the efficiency (η) can be calculated as follows:

Example: A diesel engine has a specific fuel consumption (at a certain operating point) of 198 g / kWh. The calorific value of the diesel fuel used is around 11.9 kWh / kg. The efficiency is calculated as follows:

Calorific values ​​of common fuels
Fuel type MJ / kg kWh / kg
diesel 42.9-43.1 ≈ 11.9
Regular gasoline 41.2-41.9 ≈ 11.5
Premium gasoline 41.2-41.6 ≈ 11.4
Aviation Fuel ( AvGas ) 43.5 ≈ 12.1
Kerosene 43 ≈ 11.9

It should be noted that the usual fuels consist of fuel mixtures and the calorific values ​​are therefore not constant. Examples are winter diesel, summer diesel and gasoline with different degrees of ethanol admixture.

Maps of specific fuel consumption

Example of a characteristic field of the specific fuel consumption in g / kWh (shell diagram) The axes are effective mean pressure , p e in bar (vertical), and speed, n in 1 / min (horizontal).

The specific fuel consumption - and thus the efficiency - is not a constant value, but depends on the operating state of the engine. Depending on its speed and load, different values ​​result. However, often only a single value is given. If no further explanation follows, this value is the so-called “best value”, i.e. the achievable minimum.

A characteristic field of the specific fuel consumption, which is also referred to as a “shell diagram”, is much more meaningful . In addition to the “best point”, all other values ​​at full load and at part load can also be read from this diagram.

These characteristic fields are of particular importance for the design and control of manual transmissions. By selecting the appropriate gear ratio, the engine speed and load condition can be set so that the respective minimum consumption is achieved.

Comparative values

engine Type Specific fuel consumption
[g / kWh] 		fuel
Four-stroke engine Truck / car 180-210 diesel
Four-stroke engine Car 220-250 petrol
Rotary engine Car / motorcycle 300-380 petrol
Gas turbine Cars / Aviation 300-1000 Kerosene
Pulverized coal engine Stationary engine 340-350 Coal dust
Two-stroke engine motorcycle 380-500 petrol
Steam engine steam train 965-1260 coal

Selected engines / power units

Application example Engine type year Power kW] Working principle Specific
fuel consumption
[g / kWh] 		fuel
1940s industrial engine MAN D 0534 G 1942 51.5 diesel 217.5 Gas oil
Industrial engine from the 1950s Mercedes-Benz OM 636 1952 29 diesel 286 Diesel fuel
First diesel engine - 1897 13 diesel 324 petrol
Brush cutter ( four-stroke engine ) Honda GX 35 2011 0.94 Otto 390 petrol
Chainsaw ( two-stroke engine ) Stihl MS 391 2016 3.3 Otto 421 petrol
Wankel engine for drone UAV Engines AR801 1999 30th Wankel 304 petrol
Industrial diesel engine 2000s VW EA188 1.9 l 2005 63 diesel 207 Diesel fuel
Passenger car diesel engine from the 2000s BMW N47 2007 130 diesel 198 Diesel fuel
Passenger car gasoline engine 2010s Ford EcoBoost 2011 74 Otto 240 petrol
1960s industrial engine ЯМЗ-238М2 1960s 176 diesel 214 Diesel fuel
Industrial diesel engine from the 2010s OM 936.972 2015 220 diesel 212 Diesel fuel
1930s aircraft engine BMW 114 1936 460 diesel 266 Gas oil
1940s aircraft engine Junkers Jumo 205 1940 647 diesel 211 Gas oil
Formula 1 engine 1980s Honda 1.5L 1987 559 Otto 258 Premium gasoline
Shaft turbine Klimow TW3-117 WM 1972 1.103 Joules 299 Kerosene
1940s aircraft engine Pratt & Whitney R-4360 1945 2,610 Otto 265 petrol
Turboprop Kuznetsov NK-12 1955 11,032 Joules 218.9 Kerosene
2-stroke marine diesel MAN S80ME-C9 2014 27,060 diesel 164.4 Heavy oil ISO 8217
2-stroke marine diesel Wärtsilä RT-flex96C 2008 84,420 diesel 171 Heavy oil ISO 8217
4-stroke marine diesel Wärtsilä 8V31 2015 4,480 diesel 170.6 Heavy oil ISO 8217
2-stroke HPDF marine
engine (diesel cycle, pilot ignition),
slow speed, SCR cat 		MAN 6G70ME-C9.5-GI 2021 (sim.) 21,840 diesel 139.6 + 1.3 LNG or LBM + heavy fuel oil ISO 8217
1960s boxer engine VW type 126 1969 35 Otto 306 petrol
Rotary engine of the NSU Ro80 KKM 612 1967 85 Wankel 313 petrol
Industrial engine from the 1890s Hornsby Akroyd engine 1891 5.6 Akroyd 460 Gas oil

Individual evidence

  1. ^ Bosch: Kraftfahrtechnisches Taschenbuch, 28th edition, May 2014. ISBN 978-3-658-03800-7 , p. 33.
  2. ↑ Klaus Schreiner: Basic knowledge of the internal combustion engine . 2nd Edition. Springer Fachmedien, Wiesbaden 2015, ISBN 978-3-658-06186-9 , 3.3 What does an indication of 200 g / (kWh) actually mean?
  3. ^ BOSCH (ed.): Kraftfahrtechnisches Taschenbuch . 28th edition. 2014, ISBN 978-3-658-03800-7 , p. 316 .
  4. ^ A b Bosch: Kraftfahrtechnisches Taschenbuch. 28th edition, May 2014. ISBN 978-3-658-03800-7 , p. 457.
  5. ^ A b Robert Bosch GmbH: Kraftfahrtechnisches Taschenbuch . 19th edition. 1984, ISBN 3-18-418005-0 , p. 329.
  6. ^ A b Bosch: Kraftfahrtechnisches Taschenbuch . Stuttgart, 10th edition 1950, p. 225.
  7. ^ Bosch: Kraftfahrtechnisches Taschenbuch. 26th edition, 2007. ISBN 978-3-8348-0138-8 , p. 509.
  8. ↑ Hans Kremser: The structure of high-speed internal combustion engines for motor vehicles and railcars. In: Hans List (Ed.): The internal combustion engine. Volume 11. Springer, Vienna 1942, ISBN 978-3-7091-5016-0 . P. 136
  9. ↑ Manual Mercedes-Benz OM 636, p. 45
  10. ↑ Günter Mau: Manual Diesel Engines in Power Plant and Ship Operation . Vieweg. Braunschweig / Wiesbaden. 1984. ISBN 978-3-528-14889-8 . P. 7
  11. ↑ breitband-lambda.de Studienarbeit T3100. Page 58 ff. (Performance information p. 67)
  12. ↑ dlg-test.de Stihl MS 391
  13. ↑ AR 801 50bhp
  14. ↑ TDI-Industriemotor, p. 3. ( Memento from March 12, 2017 in the Internet Archive )
  15. ↑ auto-innovations.com
  16. ↑ Ernst, R.; Friedfeldt, R.; Lamb, S.; Lloyd-Thomas, D.; Phlips, P.; Russell, R.; Zenner, T: The New 3 Cylinder 1.0L Gasoline Direct Injection Turbo Engine from Ford . In: 20th Aachen Colloquium Automobile and Engine Technology . Aachen 2011.
  17. ↑ Силовой Агрегат ЯМЗ-238М2. (Russian), accessed September 24, 2017
  18. ↑ dlg-test.de Unimog U 530
  19. ↑ Michael Trzesniowski: racing car technology . 2nd Edition. Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3-8348-0857-8 , p. 529
  20. ↑ Technical data TW3-117
  21. ^ Gerard L. Blake: Operating the Pratt & Whitney R-4360-59B. (No longer available online.) Archived from the original on November 5, 2016 ; accessed on November 6, 2016 .
  22. ↑ НК-12МП - Основные характеристики двигателя ( Memento from April 25, 2017 in the Internet Archive )
  23. ↑ MAN B&W S80ME C9, p. 50.
  24. ↑ WÄRTSILÄ RT ‑ flex96C AND WÄRTSILÄ RTA96C TECHNOLOGY REVIEW
  25. ^ Wärtsilä-31 engine
  26. ↑ SEA / LNG (Ed.): LNG as a marine fuel - The investment opportunity. In: Selbstverlag, February 24, 2020, (English). sea-lng.org , PDF, 2,450 kB, accessed on February 29, 2020.
  27. ^ VDA: Volkswagenwerk AG Wolfsburg - Type VW double cabin. Group 13, number 223b. Frankfurt am Main December 1969.
  28. ^ Matthias Parschau: Properties of Wankel Engines , accessed on April 1, 2020
  29. ^ Friedrich Sass: History of the German internal combustion engine construction from 1860 to 1918 , Springer, Berlin / Heidelberg 1962, ISBN 978-3-662-11843-6 . P. 418