Petrol engines have developed the following technologies
1. The multi-valve engine was previously limited to sports cars and motorcycles. To obtain higher output power, the number of valves used in car engines has increased.
2. The multi-cylinder engine has become more widespread. It has a smoother rotation to decrease noise and vibration.
3. Three-way catalyst (Pt-Pd-Rh alloy) technology, using O2 and knock sensors, has decreased the three components CO, HC, and NOx in the exhaust gas, to decrease environmental pollution.
4. The variable valve system has decreased fuel consumption.
5. Decreased inertial weight and electronic control have given improved engine performance.
6. Hybrid systems including an electric motor have reduced fuel consumption.
Fig.1 Development of power output of petrol engines and diesel engines.
At the end of the 20th century, automotive diesel technology has made significant progress. Diesel engines play a significant role in reducing fuel consumption in cars. In Europe, where this is already an important issue in contrast to the United States or Japan, current estimates indicate that the development target of a ‘3-litre car’ can only be implemented with a diesel engine. The diesel output power for a passenger car as well as for big commercial vehicles is likely to increase. As shown in Fig. 1 the specific power output range of diesels now equals that of naturally aspirated petrol engines. The average output power is 50 kW/L. Most of the direct-injection diesel engines for cars around the year 2003 have reached specific power outputs of up to about 60 kW/L. Diesel cars are now available with power outputs to 180 kW and levels of low speed torque that were previously unimaginable. A truck using a large diesel engine has a maximum power around 400 kW.
These engines are characterized by four valves per cylinder, a combustion bowl located centrally in the piston and second-generation high-pressure injection systems (common rail, unit injector) with efficient control of the injection process by electronic means. The common rail technology provides better fuel efficiency, and better torque at low speeds. The increase in performance is combined with an increase in cylinder pressures up to peak values of 18 MPa.
The additional air supply by exhaust gas circulation also offers the possibility of very high specific power outputs, which will stretch the performance and fuel economy boundaries even further. The more stringent NOx limit requires additional after-treatment technology, and particulate filters will become the norm for diesel engine applications in cars.
The use of diesel engines remains on a continuing upward trend. The reason behind the explosion in the European market for diesel engines is generally to do with rapid advances in technology rather than simple fuel economy. Technology has now given diesel engines high performance and favorable torque characteristics.