Licensed from Columbia University Press
Applications
Petrol engines have many applications, including:
- Motor cars
- Motorcycles
- Aircraft
- Motorboats
- Small machines, such as lawn mowers, chainsaws and portable Engine-generators
Design
Working cycles
Petrol engines may run on the four-stroke cycle or the two-stroke cycle. For details of working cycles see:
Cylinder arrangement
Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in V-formation. Alternatives include Rotary and Radial Engines the latter typically have 7 or 9 cylinders in a single ring, or 10 or 14 cylinders in two rings.
Cooling
Petrol engines may be air-cooled, by fins on the cylinders, or liquid-cooled, by a water jacket and radiator. The coolant was formerly water but is now usually a mixture of water and ethylene glycol. This mixture has a lower freezing-point and a higher boiling-point than pure water. In addition, the cooling system is usually slightly pressurized to minimise evaporation of coolant.
Compression ratio
The compression ratio is the ratio between the cylinder volumes at the beginning and end of the compression stroke. Broadly speaking, the higher the compression ratio, the higher the efficiency of the engine. However, compression ratio has to be limited to avoid pre-ignition of the fuel-air mixture which would cause engine knocking and damage to the engine. Modern motor-car engine generally have compression ratios of between 9:1 and 10:1, but this can go up to 11 or 12:1 for high-performance engines that run on, say, 98 R0N (93 AKI, US Premium- or European Super-grade) petrol. In the 1950s, with low-octane fuel and less well-designed cylinder heads, compression ratios were between 6.5:1 and 7:1. Old tractor engines running on tractor vaporising oil might have compression ratios as low as 4.5:1 but modern tractors have diesel engines.
Ignition
- main article Ignition system
Future
Concerns about global warming and air pollution have put a question mark over the future of the petrol engine. Much has been done to improve its fuel efficiency and reduce emissions and this has bought it more time.
Sources
- Linked Wikipedia articles
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Last updated on Friday July 25, 2008 at 11:38:13 PDT (GMT -0700)
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