Mobile Sources. Mobile sources. Gasoline car: 4-strokes Diesel car Automobile : 4-strokes, 2-strokes. Animated scheme of a four stroke internal combustion engine, Otto principle : Intake stroke - Air and vaporized fuel are drawn in.
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Animated scheme of a four stroke internal combustion engine, Otto principle:
The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream.
To more easily comply with emissions regulations, automobile manufacturers began installing fuel injection systems in more gasoline engines during the late 1970s.
Since the early 1990s, almost all gasoline passenger cars sold in first world markets are equipped with electronic fuel injection (EFI). The carburetor remains in use in developing countries where vehicle emissions are unregulated and diagnostic and repair infrastructure is sparse. Fuel injection is gradually replacing carburetors in these nations too as they adopt emission regulations conceptually similar to those in force in Europe, Japan, Australia and North America.
In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop control -- it was not feasible to achieve this control with carburetors.
When you step on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU, the computer that controls all of the electronic components on your engine) "sees" the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it.
Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.
These main areas of emissions are classified as evaporative, exhaust, and refuelinglosses. Evaporation of gasoline is a source of volatile organic compounds (VOC’s) comparable in magnitude to the exhaust VOC’s emissions.
grams per mile hydrocarbons (HC), 3.6 grams per mile
nitrogen oxides (NOx), and 87 grams per mile carbon
The current Federal certification standards for
exhaust emissions from cars are 0.25 gram per mile HC, 0.4
gram per mile NOx, and 3.4 grams per mile CO.