Turbocharging technology and EGR Recently, in order to increase the thermal efficiency and output power of a diesel engine, high-pressure injection has been used for direct injection, and high torque has been achieved by high pressurization. The turbocharged diesel engine that can obtain high torque in the commonly used low-medium-speed field is more likely to achieve small-displacement quantification than the gasoline engine, and the low-speed cruising in high-speed cruising provides better fuel economy. With VG turbocharging, not only can the car's ideal flat torque curve be obtained, but also black smoke at low speeds and improved acceleration can be reduced. In addition, recent studies have used double-stage turbocharging to compensate for the lack of air volume during acceleration. From the perspective of reducing exhaust emissions, it is expected that higher pressure and higher EGR will be required in the future. EGR is a very effective technique for reducing NOx.
Common-rail injection technology Among the new technologies, the most effective for diesel engines is the common-rail injection system. The increase in the maximum injection pressure of the common rail injection system and the shortening of the minimum injection interval have made rapid progress. A micro-equivalent fuel with less than one drop of eye drops per cycle can generate a pressure of nearly 2,000 atmospheres, and inject the technology in several fractions of a microsecond period to shock the world. Recently, the drive of the injector controller has been changed from an electromagnetic type to a piezoelectric type, and the responsiveness of the control valve has been doubled. In the future, the common rail fuel will be further pressurized in the booster piston in the injector, and the injection pressure may exceed 2,000 atmospheres.
Engine Combustion Technology Uniform premixed compression ignition (HCCI) combustion technology, which has been studied for more than 10 years, is not practical for high loads. It is only used in the partial load areas where the exhaust gas temperature is low and the aftertreatment purification rate is low. Therefore, it is considered as an effective way to take a normal dual-mode operation of diesel combustion at a high load and an extremely low load near no load. This mode of conversion can also be achieved using common rails. Since the operation of this part of the load is set at an injection period closer to the compression top dead center, even if the premixing is not uniform, the so-called "premixed combustion" is more accurate than the "HCCI combustion". . In addition, in the normal combustion mode near the no-load range, even if the NOx is limited by the EGR, the PM emission level is also low, so the premixed combustion that is increased compared to the unburned HC and the CO is more advantageous.
Exhaust After-Treatment Technology The combustion technology of engines such as EGR and common-rail alone is unlikely to enable both NOx and PM to meet Japan's current new long-term emissions regulations. Exhaust aftertreatment will take over the main task of diesel engine exhaust purification. PM uses DPF purification to reduce emissions. In order to reduce NOx emissions, new technologies for SCR or NSR purification will be adopted.
Diesel Engine Hybrids Now the city is basically a gasoline engine. In order to further improve fuel economy, it is very necessary to use diesel hybrid vehicles. The latest diesel hybrid buses are very effective in terms of fuel consumption and exhaust emissions. And it is very likely due to passenger cars.
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