For neutralization of exhaust gases gasoline engine used catalytic Converter. But as this task decide on diesels?
In the petrol engine, the catalyst is effectively converting toxic CO, SN, NOX to harmless components of CO2, H2O and N2. For short-term variations of the fuel-air mixture from optimal or ignition violations, the microparticles of unburned carbon may appear-it is easier to say, soot. But as long as there are no serious problems, its share in the exhaust is low and the catalyst is burned to the carbon dioxide. There is no black smoke in the car. With the diesel engine fumes, it's not that simple! When working with small loads, the temperature of the gas at the inlet to the catalyst is much lower than that of a petrol engine, and soot is simply not able to burn. But throwing the carcinogens into the atmosphere is a bad tone, and has received a diesel-specific diesel-special, particulate filter. On modern engines, both knots are located in a single casing, which is located near the engine. Next because the closer to the vent valves, the higher the exhaust temperature is required for the effective operation of the cleaning system. Diesel engine exhaust system: 1-engine control unit; 2-mass flow sensor; 3-gas temperature sensor for turbocharger; 4-turbocharger; 5 and 9-gas temperature sensors before and after the particulate filter; 6-Mixer composition sensor (broadband oxygen sensor); 7-filter-neutralizer; 8-gas-pressure differential sensor; 10-silencer. However, with time, the filter is gradually filled with soot. To prevent her from pluggedin a hundredth, she needs to get rid of it periodically, burning it. There are two ways. The first engine management system does not interfere with the work process-it is called passive regeneration. It flows at the gas temperature at the inlet to the filter no less than 350 degrees, in the presence of a catalyst-platinum on its pottery. The latter are similar to the well known hundredths of modern neutralers, but have a significant difference shown in figure. 2. The channels are divided into intake and exhaust. The first, open by the engine, receive gases with all the bouquet of poisonous substances, including soot. The second is open from the opposite side-the purified soot gases are moving on to the catalyst. The channels are located in the chess order and are separated by fine filter walls, impermeable to soot (it remains in inlet) but propelling gases. Their material is a porous silicon carbide, coated with a mixture of aluminium oxide and cerium oxide, it is a reference surface for the platinum layer. The design of the channels (hundredth) of the particulate filter: Sage is racing in the outlet channels, and the gases, passing through porous walls, go to the exhaust outlets. The temperature of the exhaust gas required for the burning is not always possible in the diesel engine-at low loads in cylinders there is a lot of air, and the fuel is not enough! Enough heat is available only in case of work at relatively high capacity-for example, at 60-80 km/h, or even higher. But this is often impossible, especially in the city, and there is no self-cleaning of the particulate filter. If you rely only on it, then soot will completely purchase the intake channels (honeycomb) and the work processes in the engine will be broken. To prevent this from happening, you need to get rid of the soot, and keep the high temperature of the gas inside the particulate filter. The second way to clean the filter is active regeneration. If necessary (below), the engine control unit begins to supply some additional fuel to the cylinders after the primary dose, shortly before the opening of the valve. The "extra" straw is not able to work and goes to the particulate filter, where in the presence of platinum is burned. The temperature of the gases is increased and soot is actually burned on the command of the control unit. Let' s get back to rice. 1. Control unit 1 needs to be decided when and at what time to turn on the active regeneration of the filter. But how does he do that? It's very simple: to drop the gas pressure on the neutralizer. To this end, tubes connected to the 8 pressure drop sensor are built on both sides. Regeneration will be activated when the delta exceeds a given value. It usually lasts 10 to 15 minutes. It's not that simple. The pressure drop on the particulate filter is related to the exhaust flow rate, which in turn depends on their temperature. Therefore, temperature sensors 5 and 9 are installed before and after the particulate filter. Of course, for completeness, the control unit takes account of the mass air flow rate, the 2 of which is traditionally placed in the inlet pipe. There's a 3 more sensor on the engine exhaust. It tracks the exhaust gas temperature at the compressor inlet. If it is close to the limit that can be overheated and the destruction of a very expensive hub, the control unit will limit the supply of the fuel-and the temperature will decrease. The cleaning of the filter is of course most effective when air/fuel ratio gases are obtained. The control unit controls the composition of the mixture, based on the data of the broadband oxygen sensor (mixture sensor) 6, which monitors the oxygen content of the exhaust. Finally, after reworking all the information obtained, the control unit adjusts the fuel feed into the engine cylinders. The state of all components responsible for the treatment of exhaust gases is controlled by the Self-diagnosis system. If the malfunction is detected, Smoke Engine will be lit. For example, in traffic jams due to low exhaust temperature, despite all the control unit's efforts, the regeneration does not start! The filter is filled with soot-and in combination, the signal with the filter (if it is provided by the design) or the lamp "check the engine" is flashing. Then it's time to try to burn the soot in a passive way-drive ten-fifteen minutes at higher capacity. If after that the control lamp does not go out, we will have to go to the "chimney sweep" service.