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A gas engine is an internal combustion engine which runs on a gas fuel, such as coal gas, producer gas, biogas, landfill gas or natural gas. In the UK, the term is unambiguous. In the US, due to the widespread use of "gas" as an abbreviation for gasoline, such an engine might also be called a gaseous-fueled engine or natural gas engine.
Generally the term gas engine refers to a heavy-duty industrial engine capable of running continuously at full load for periods approaching a high fraction of 8,760 hours per year. Unlike a gasoline automobile engine, which is lightweight, high-revving and typically runs for no more than 4,000 hours in its entire life. Typical power ranges from 10 kW (13 hp) to 4,000 kW (5,364 hp).
There were many experiments with gas engines in the 19th century but the first practical engine was built by the Belgian engineer Étienne Lenoir in 1860. His work was further researched and improved by a German engineer Nikolaus August Otto, now recognised as the inventor of the first 4-stroke internal-combustion engine to efficiently burn fuel directly in a piston chamber. In August 1864 Otto met Eugen Langen who, being technically trained, glimpsed the potential of Otto's development, and one month after the meeting, founded the first engine factory in the world, NA Otto & Cie. At the 1867 Paris World Exhibition their improved engine was awarded the Grand Prize
The best-known builder of gas engines in the UK was Crossley, but there were several other firms based in the Manchester area as well. Tangye Ltd. sold its first gas engine, a 1 nominal horsepower two-cycle type, in 1881, and in 1890 the firm commenced manufacture of the four-cycle gas engine. 
The Anson Engine Museum in Poynton, near Manchester, England, has a collection of engines that includes several working gas engines, as well as the first UK-built diesel engine by Mirrlees, Bickerton and Day.
British engines mentioned above were of the slow-speed type—less than 1000 rpm—and used pilot diesel injection for ignition. Modern gas engines are of the high-speed type—1500 rpm—and use spark ignition. British manufacturers did not invest in developing the technology and were superseded by more forward-thinking suppliers.
Current manufacturers 
Manufacturers of gas engines include Rolls-Royce with the Bergen-Engines AS, Kawasaki Heavy Industries, MTU Friedrichshafen, GE Jenbacher, Caterpillar Inc., Perkins Engines, MWM, Cummins, Wärtsilä, GE Energy Waukesha, Guascor Power, Deutz, MTU, MAN, Fairbanks Morse, Doosan, and Yanmar. Output ranges from about 10 kW (13 hp) micro CHP [combined heat and power] to 18 MW (24,000 hp). Generally speaking, the modern high-speed gas engine is very competitive with gas turbines up to about 50 MW (67,000 hp) depending on actual circumstances, and the best ones are much more fuel efficient than the gas turbines. Rolls-Royce with the Bergen Engines, Caterpillar and many other manufacturers base their products on a diesel engine block and crankshaft. GE Jenbacher are the sole company whose engines are designed and dedicated to gas alone.
Typical applications 
Typical applications are baseload or high-hour generation schemes, including combined heat and power, landfill gas, mines gas, well-head gas and biogas (where the waste heat from the engine may be used to warm the digesters). For typical biogas engine installation parameters see. For parameters of a large gas engine CHP system, as fitted in a factory, see. Gas engines are rarely used for standby applications, which remain largely the province of diesel engines. One exception to this is the small (<150 kW) emergency generator often installed by farms, museums, small businesses, and residences. Connected to either natural gas from the public utility or propane from on-site storage tanks, these generators can be arranged for automatic starting upon power failure. The natural gas engines (LNG) are getting more into the marine market, as the lean-burn gas engine can meet the new emission requirements without any extra fuel treatment or exhaust cleaning systems.
Use of methane or propane gases 
Since natural gas (methane) has long been a clean, economical, and readily available fuel, many industrial engines are either designed or modified to use gas, as distinguished from gasoline. Although the carbon emission footprint does not differ significantly, their operation produces less complex-hydrocarbon pollution, and the engines have fewer internal problems. One example is the liquefied petroleum gas (propane) engine used in vast numbers of forklift trucks. Common usage of "gas" to mean "gasoline" requires the explicit identification of a natural gas engine. (There is also such a thing as "natural gasoline", but this term is very rarely observed outside the refining industry.)
Technical details 
A gas engine differs from a petrol engine in the way the fuel and air are mixed. A petrol engine uses a carburetor or fuel injection but a gas engine often uses a venturi system to introduce gas into the air flow. Early gas engines used a three-valve system, with separate inlet valves for air and gas.
The weak point of a gas engine compared to a diesel engine is the exhaust valves, since the gas engine exhaust gases are much hotter for a given output, and this limits the power output. Thus a diesel engine from a given manufacturer will usually have a higher maximum output than the same engine block size in the gas engine version. The diesel engine will generally have three different ratings - Standby, Prime, and Continuous, (UK, 1 hour rating, 12 hour rating and continuous rating) whereas the gas engine will generally only have a Continuous rating, which will be less than the Diesel Continuous rating
Energy balance 
Mechanical efficiency 
Gas engines that run on natural gas have typically a mechanical efficiency between 35-45%., the best engines can achieve an mechanical efficiency of slightly more than 48%. These gas engines are usually medium speed engines Bergen Engines Fuel energy arises at the output shaft, the remainder appears as waste heat. Large engines are more efficient than small engines. Gas engines running on biogas typically have a slightly lower efficiency (~1-2%) and syngas reduces the efficiency further still. GE Jenbacher's recent J624 engine is the world's first 24 cylinder gas engine with a high efficiency running on methane.
When considering engine efficiency one should consider whether this is at the lower heating value or higher heating value of the gas. Engine manufacturers will typically quote efficiencies at the lower heating value of the gas, i.e. the efficiency after energy has been taken to evaporate the intrinsic moisture within the gas itself. Gas distribution networks will typically charge based upon the higher heating value of the gas (i.e. total energy content).
Combined heat and power 
Engine reject heat can be used for building heating or heating a process. In an engine, roughly half the waste heat arises (from the engine jacket, oil cooler and after-cooler circuits) as hot water which can be at up to 110 °C. The remainder arises as high-temperature heat which can generate pressurised hot water or steam by the use of an exhaust gas heat exchanger.
Engine cooling 
Some engines (air or water) have an added oil cooler.
Cooling is required to remove excessive heat, over heating can cause engine failure, usually from wear, cracking or warping.
Gas Consumption Calculation 
The formula shows the gas flow requirement of a gas engine in norm conditions at full load.
- is the gas flow in norm conditions
- is the engine power
- is the mechanical efficiency
- LHV is the Low Heating Value of the gas
Gallery of Historic Gas Engines 
See also 
- CHP Directive
- Gas turbine
- History of the internal combustion engine
- List of natural gas vehicles
- Tables of European biogas utilisation
- Gas engine specifications www.clarke-energy.com, accessed 4.01.2013
- "The Basic Industries of Great Britain by Aberconway - Chapter XXI". gracesguide.co.uk. Retrieved 2010-06-05.
- , Retrieved 27.02/09
-  caterpillar-bio-gas-engine-fitted-to-long-reach-sewage-works-thames water
- Gas Engines, www.clarke-energy.com, Accessed 1 April 2011
- GE Jenbacher J624, Retrieved 27.02/09
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