CO2Facts.info about carbon dioxide and biogas
Biogas-Engines
Typical applications
A gas engine means an engine running on a gas, such as coal gas, producer gas biogas, landfill gas, or natural gas.
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 whitout 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. Common usage of "gas" to mean "gasoline" requires the explicit identification of a natural gas engine.
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
Two fuels
A gas engine can be designed to run on gas, or liquid diesel fuel, or a mixture of the two. There are two different configurations:
Dual fuel engine
This can run on diesel fuel alone, or a mixture of gas and diesel fuel. It cannot run on gas alone because it has no spark ignition system. But as it is not a pure gas, neither a pure diesel designed engine it have some dissadvantages when it comes to fuel efficiency, and allso Methane slip. The fuel efficiency may be 5-8% less than in a comparable lean burn spark ignited engine at 100% load, and even more on lower loads.
Alternative fuel engine
This can run on diesel fuel 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.
(Quelle: Wikipedia)