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A gas engine means an engine running on gas, such as coal gas, producer gas biogas, landfill gas, or natural gas. In the UKmarker, the term is unambiguous. In the USmarker, due to the widespread use of "gas" as an abbreviation for gasoline, such an engine might also be called a gaseous fuelled engine or a spark ignited engine.

Generally the term gas engine refers to a heavy duty, slow revving industrial engine capable of running continuously at full output for periods approaching a high fraction of 8,760 hours per year, for many years, with indefinite lifetime, unlike say a gasoline automobile 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 to 4,000 kW.

History

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 . The best known builder of gas engines in the UKmarker was Crossley, but there were several other firms based in the Manchestermarker area as well.

The Anson Engine Museummarker in Poyntonmarker, near Manchester, Englandmarker, has a collection of engines that includes several working gas engines, as well as the first UK-built Diesel engine by Mirrlees.

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 British manufactures did not invest in developing the technology and were superseded by more forward-thinking suppliers.

Current manufacturers

Manufacturers of gas engines include GE Jenbacher, Caterpillar Inc., Perkins Engines, MWM, Cummins and Wärtsilä Waukesha, Guascor, Deutz, MTU, MAN. Output ranges from about 50 kW to 4MW. Generally speaking, the modern high-speed gas engine is competitive with gas turbines up to about 5 MW depending on actual circumstances. Caterpillar and many other manufacturers are based 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, mine gas, well-head gas and biogas (where the waste heat from the engine may be used to warm the digesters) and landfill gas. 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 (<150KW) emergency="" generator="" often="" installed="" by="" farms,="" museums,="" small="" businesses,="" and="" residences.="" Connected="" to="" either="" natural="" gas="" from="" the="" public="" utility="" or="" propane="" on-site="" storage="" tanks,="" these="" generators="" can="" be="" arranged="" for="" automatic="" starting="" upon="" power="" failure.=""></150KW)>

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 meaningfully, 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. Regrettably, 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

Electrical efficiency

Gas engine linked to generators that run on natural gas are typically between 35-45% electrically efficient. Fuel energy arises at the output shaft, the remainder appears as waste heat. Higher efficiencies are achieved in larger engines than smaller 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.

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 110oC. The remainder arises as high temperature heat which can generate pressurised hot water or steam by the use of an exhaust gas heat exchanger.

Two fuels

A gas engine can be designed to run on gas, or oil, or a mixture of the two. There are two different configurations.

Dual fuel engine

This can run on oil alone, or a mixture of gas and oil. It cannot run on gas alone because it has no spark ignition system.

Alternative fuel engine

This can run on oil or gas but not a mixture of the two. When running on oil, it uses compression ignition as in a diesel engine. When running on gas it uses spark ignition. The term "Bi-fuel" may be preferable to "Alternative fuel" because the latter term is, nowadays, often used to mean any non-petroleum fuel.

External links and references

  1. http://library.thinkquest.org/C006011/english/sites/gasmotoren.php3?v=2
  2. GE Jenbacher J624, Retrieved 27.02/09
  3. [1]caterpillar-bio-gas-engine-fitted-to-long-reach-sewage-works-thames water
  4. http://www.claverton-energy.com/first-energy-offer-excellent-condition-complete-gas-engined-chp-system-for-sale-and-installation.html


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