HistoryAutomobiles were first manufactured with exhaust emissions control systems in 1966. Since then, technology has undergone several advancements that have increased the efficiency of the internal combustion engine. Older emission control systems inject air into the exhaust manifold which are known as, air injection reactor (AIR.) The catalytic converter was developed in the early 1970's when severe air pollution was widespread and was made mandatory by the US government in 1976. An EGR valve is used is to lower KNOX (NO2) gases which occur when the combustion chamber when temperature reaches over 3500.
During normal vehicle operation, emissions are produced. While some of these emissions are harmless like water, heat, and oxygen, harmful byproducts—hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxide (NOx)—are also produced. One way the system reduces these harmful byproducts is by making the engine run more efficiently. The emissions system also recycles emissions back through the combustion process or converts them into harmless gases.
NOx sensors represent state of the art technology that can be applied to gasoline lean burn engines as part of a broader engine control or diagnostic system used to insure proper operation of the NOx emission control system. These sensors can be incorporated independent of the NOx emission control technology used on the vehicle and their function is primarily to monitor the NOx conversion efficiency of the catalyst. The sensors can work as part of a feedback loop to the control unit on the emissions system to make real time adjustments and optimize NOx conversion. The principle of operation of one type of NOx sensor is based on proven solid electrolyte technology developed for oxygen sensors. The dual chamber zirconia sensing element and electro-chemical pumps work in conjunction with precious metal catalyst electrodes to control the oxygen concentration within the sensor and convert the NOx to nitrogen. The sensor sends output signals in volts that are directly proportional to ppm NOx concentration. The sensors can be incorporated upstream and downstream of the catalyst, for example, to provide a feedback control loop to the ECU of the emissions system. The ECU can than make adjustments to optimize NOx conversion performance. The ECU can than make adjustments to optimize NOx conversion performance. In the case of SCR technology, feedback can also be provided to the urea dosing system whereas in the case of lean NOx trap technology a feedback loop could signal the regeneration of the trap.