Car and Environmental impact - Wikipedia
While there are different types of fuel that may power cars, most rely on gasoline or diesel. The United States Environmental Protection Agency states that the average vehicle emits 8,887 grams of carbon dioxide per gallon of gasoline. The average vehicle running on diesel fuel will emit 10,180 grams of carbon dioxide.49 Many governments are using fiscal policies (such as road tax or the US gas guzzler tax) to influence vehicle purchase decisions, with a low CO2 figure often resulting in reduced taxation.50 Fuel taxes may act as an incentive for the production of more efficient, hence less polluting, car designs (e.g. hybrid vehicles) and the development of alternative fuels. High fuel taxes may provide a strong incentive for consumers to purchase lighter, smaller, more fuel-efficient cars, or to not drive. On average, today's cars are about 75 percent recyclable, and using recycled steel helps reduce energy use and pollution.51 In the United States Congress, federally mandated fuel efficiency standards have been debated regularly, passenger car standards have not risen above the 27.5 miles per US gallon (8.6 L/100 km; 33.0 mpg-imp) standard set in 1985. Light truck standards have changed more frequently, and were set at 22.2 miles per US gallon (10.6 L/100 km; 26.7 mpg-imp) in 2007.52
Diagram of uniflow scavenging
Using a separate blower avoids many of the shortcomings of crankcase scavenging, at the expense of increased complexity which means a higher cost and an increase in maintenance requirement. An engine of this type uses ports or valves for intake and valves for exhaust, except opposed piston engines, which may also use ports for exhaust. The blower is usually of the Roots-type but other types have been used too. This design is commonplace in CI engines, and has been occasionally used in SI engines.
CI engines that use a blower typically use uniflow scavenging. In this design the cylinder wall contains several intake ports placed uniformly spaced along the circumference just above the position that the piston crown reaches when at BDC. An exhaust valve or several like that of 4-stroke engines is used. The final part of the intake manifold is an air sleeve which feeds the intake ports. The intake ports are placed at an horizontal angle to the cylinder wall (I.e: they are in plane of the piston crown) to give a swirl to the incoming charge to improve combustion. The largest reciprocating IC are low speed CI engines of this type; they are used for marine propulsion (see marine diesel engine) or electric power generation and achieve the highest thermal efficiencies among internal combustion engines of any kind. Some Diesel-electric locomotive engines operate on the 2-stroke cycle. The most powerful of them have a brake power of around 4.5 MW or 6,000 HP. The EMD SD90MAC class of locomotives use a 2-stroke engine. The comparable class GE AC6000CW whose prime mover has almost the same brake power uses a 4-stroke engine.
An example of this type of engine is the Wärtsilä-Sulzer RTA96-C turbocharged 2-stroke Diesel, used in large container ships. It is the most efficient and powerful internal combustion engine in the world with a thermal efficiency over 50%.9101112 For comparison, the most efficient small four-stroke engines are around 43% thermally-efficient (SAE 900648);citation needed size is an advantage for efficiency due to the increase in the ratio of volume to surface area.
See the external links for a in-cylinder combustion video in a 2-stroke, optically accessible motorcycle engine.
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