Technology for Cleaner Diesel

PM and NOx Simultaneous Reduction

Electronic Control System
When the combustion temperature is higher, and the fuel/air mixture is closer to complete combustion, greater NOx generates in emission. In other words, the more efficiently fuel is burned in order to obtain higher output, the greater amount of NOx generated. However, if the combustion temperature is lowered, this results in reduced output and lower fuel efficiency. So in order to reduce NOx generation, the engine has to control explosive combustion and complete the combustion cycle calmly. By controlling the fuel injection amount and timing using an electronic control system, a diesel engine can achieve well-balanced combustion, thereby producing clean, low NOx emissions while maintaining performance.

Common Rail High-Pressure Fuel Injection System
A common rail
Isuzu's electronically controlled common rail high-pressure fuel injection system performs fuel injection at a higher pressure than the conventional high-pressure system to reduce the amount of PM generated during combustion. At the same time, the system cuts NOx emissions by using an electronic control unit (ECU) to precisely adjust the pressure, timing and period of fuel injection.

System Construction
This system consists of a supply pump, common rail, injector, control unit and a variety of sensors.
(1) The fuel pressure is raised to a high level up to 120 MPa by the supply pump, then delivered under pressure to a small reservoir called the common rail that temporarily holds the fuel before delivering it to each of the injectors simultaneously.
(2) The ECU detects the engine's running condition and sends signals to the injectors to control the amount of fuel and the injection timing for optimized injection.
(3) The injector injects fuel in response to ECU and optimum fuel injection is maintained at all times. With a conventional injection pump, the injection pressure varies in accordance with the engine speed and the injection amount.

Common Rail System Chart

Engine Revolution and Injection Pressure
In a conventional injection pump, it is difficult to raise the injection pressure in the low revolution range, because the injection pressure is proportional to the engine revolution. For this reason, conventional injection pumps employ fuel injection nozzles with small diameter outlets. The common rail system can control the injection pressure flexibly regardless of the engine revolution, and it realizes clean exhaust regardless of the running condition.