EGR Valve

The Exhaust Gas Recirculation (EGR) valve sends some of the exhaust gas back into the cylinders to reduce combustion temperature. This is required because nitrous oxides (nasty pollutants) form when the combustion temperature gets above 2,500 degrees F. This is as a result of the formation of nitrous oxides when the nitrogen in the air mixes with the oxygen. When it's sunny, the nitrous oxides from the exhaust get together with the hydrocarbons in the air to form smog. This is when the EGR valve comes in handy. By recirculating some of the exhaust gas back through the intake manifold to the cylinders, we can lower the combustion temperature. Lowering the combustion temperature lowers the amount of nitrous oxide produced. Consequently, less of it comes out the tail pipe. There are two types of EGR valves. One operates through the use of a vacuum, and the other operated through the use of pressure. Both types allow the exhaust gas in to lower the combustion temperature when it gets too high.

Electric Fuel Pump

Used previously for heavier vehicles, they have only recently become operational in cars. The replacement types usually use a diaphragm arrangement like the mechanical pumps, except that it is actuated by an electrical solenoid. It uses a small turbine wheel driven by a constant speed electric motor. The entire unit is located in the fuel tank and submerged in the fuel itself. When the engine is running the pump pump operates continuously, thus exerting a constant pressure which supplies the maximum fuel demands of the engine. When less fuel is required, the pump does not deliver at full potential, because the turbine is not a positive displacement type like the mechanical pump. Consequently, the turbine will run without pumping fuel and so, needs no means of varying fuel delivery rate like its mechanical counterpart. Since the fuel can flow past the spinning turbine blades, there is no need for pump inlet and outlet valves nor is there any need to vary its speed. A relay for the electric fuel pump is used to complete the circuit to the fuel pump. This cuts off current to the fuel pump in the event of an accident.

Electronic Fuel Injection

Injectors are opened by solenoids operated by an electronic control unit, as opposed to mechanical injection systms. Since the fuel has no resistance to overcome, other than insignificant friction losses, the pump pressure can be set at very low values, consistent with the limits of obtaining full atomization with the type of injectors used. The control unit, depending on the operating conditions of the engine, determines the amount of fuel to be injected. The conditions depend on manifold pressure, accelerator enrichment, cold-start requirements, idling conditions, outside temperature and barometric pressure. The systems work with constant pressure and with ‘variable timed’ or ‘continuous flow’ injection. The advantages. To begin with, it has fewer moving parts, no need for ultra-precise machining standards and quieter operation. Also, there is less power loss, a low electrical requirement, no need for special pump drives, no critical fuel filtration requirements, no surges or pulsations in the fuel line. More than anything else, it costs lesser than its mechanical counterpart.

Evaporator

The evaporator is a long tube, or coil, that goes back and forth through a multitude of cooling fins. The refrigerant is a liquid when it enters the evaporator. A fan blows warm air over the evaporator and causes the liquid refrigerant to boil. After it has absorbed the heat from the warm air, the warm air isn't warm anymore. The same blower that blows the warm air (that is now "cool" air) over the evaporator, keeps on blowing it into the interior of your car, and you have -- air conditioning! The evaporator also removes the moisture from the air coming through its fins and turns it into water. The water just drains off. The temperature of the evaporator coil can go from 33 degrees F to 0 degrees F. If it goes below 32 degrees F, the moisture that's supposed to drain off the coils will freeze. This makes for a very (surprise!) inefficient system, so a thermostatic switch is used to connect and disconnect it to the compressor as necessary.

Exhaust Manifold and Header

Usually constructed of cast iron, the exhaust manifold is a pipe that conducts the exhaust gases from the combustion chambers to the exhaust pipe. It has smooth curves in it for improving the flow of exhaust. The exhaust manifold is bolted to the cylinder head, and has entrances for the air that is injected into it. It is usually located under the intake manifold. A header is a different type of manifold; it is made of separate equal-length tubes.