Air induction system:
An internal combustion engine needs air to run. This air supply is drawn into the engine by the vacuum created during the piston’s intake stroke. Controlling the air flow is the job of the air induction system. The introduction of emission standards and fuel economy standards encouraged the development of intake air temperature controls.
The air intake system has been designed by the car manufacturer to provide a balance of airflow, sound tuning and packaging capabilities. It is responsible for supplying the engine with sufficient air to ensure optimal combustion. Key components of the air intake system include:
– Air inlet tube
– Air intake resonator
– Air filter housing
– Air filter
– Mass airflow sensor
– Evaporative emissions purge valve
– Accelerator pedal
– Throttle body
– Intake plenum
– Various vacuum hoses
The air intake tube sucks air. The air then proceeds down into the air resonator box, mounted behind the bumper, below the headlights. The resonator will reduce any unwanted sounds and tunes the intake to match the vehicle’s characteristics. The air then travels to the air box, where it is passed through an air filter. The filter is designed to maximize filtration area, with a corrugated felt pattern. The mass air flow sensor and EVAP purge valve are also mounted to the air filter box. The EVAP purge valve is a simple check valve that allows air to be vented to the intake system from the gas tank. It is activated by a solenoid which is controlled by the ECU. Enough ventilation will enrich the air with gasoline vapors before it enters the intake manifold and the engine. The Mass air flow sensor, or MAF sensor, is responsible for detecting how much air is flowing through the intake. There are two resistors inside upon which the air flow and cool down when a current is applied. When more air flows past, it cools further, decreasing resistance and increasing the current. The ECU will detect the change in current and correlate it to density (and hence mass) of air flowing through the sensor. According to the ideal gas law, the pressure can go up or the temperature can drop accordingly, but the MAF sensor can still determine the mass of air flowing through. This is ideal for automotive applications, where atmospheric conditions can vary drastically. The MAF sensor is also fitted with an intake air temperature sensor or IAT sensor to tell the ECU how warm or cold the incoming air is. The throttle body controls how much air enters the air intake manifold through a butterfly valve. The accelerator pedal opens the throttle body with a cable linkage. Many newer vehicles use a drive – by – wire setup, where the gas pedal has an electronic linkage via an electric motor to open the throttle plate. The throttle body also has various connections to vacuum lines, as well as the idle air control valve below, two coolant lines to prevent freezing, and the throttle position sensor. The air intake manifold distributes the air from the throttle body across all the pistons. It is made up of a casted section where the throttle body mounts, and aluminum tubing that is bent to shape. Newer vehicles use plastic intake plenums to save weight and reduce cost.
Emission control systems:
Emission controls have one purpose and that is to reduce the amount of pollutants and environmentally damaging substances released by vehicles. There are three main automotive pollutants: HC, carbon monoxide (CO), and NOx. Particulate (soot) emissions are also present in diesel machine exhaust. HC emissions are caused largely by unburned fuel from the combustion chambers. HC emission can also originate from evaporative sources such as the gasoline tank. CO emission are a by-product of the combustion process, resulting from incorrect air-fuel mixtures. NOx emissions are caused by nitrogen and oxygen uniting at cylinder temperatures above 2,300°F (1,261 °C). Current concerns include carbon dioxide (CO2), which is said to contribute to global warming.
The objective of the EGR valve is to reduce the polluting emissions of NOx on gasoline and diesel engines, this is achieved by the fact that it reduces the combustion temperature in the engine (the gases contain less oxygen and therefore the combustion is necessarily less hot, a bit like when you smother a fire). The principle is quite simple since it involves reinjecting part of the exhaust gases into the combustion chambers. The proportion of reinjected gas varies from 5 to 40% depending on the engine use. The consequence is the cooling of the combustion in the cylinders by reducing the oxygen rate, which mechanically reduces NOx. In fact, depending on the engine speed, the valve directs more or less gas through a small flap / movable valve controlled by the computer.