Use of Late IVC and EGR to Enhance Diesel Engine Optimization

Kapitel i bok, 2015

The increasing demand for improved efficiency of diesel engines requires more advanced combustion solutions. In addition to traditional methods such as EGR, turbocharging and advanced injection systems, variable valve timing is now available at a reasonable production cost. The use of variable inlet valve timing provides an efficient way for Low-Temperature Combustion (LTC) which provides high thermal efficiency in combination of low emission levels. Furthermore, by modifying the characteristics of the charge air (i.e. by means of EGR, boost pressure and late inlet valve closing, LIVC), further hardware optimization becomes possible, e.g. by increasing compression ratio without reaching critical peak pressures. In the present study, the effect of LIVC was investigated together with the effect of EGR in a single cylinder heavy duty diesel engine. The engine was equipped with pneumatically controlled inlet valves and a high pressure common rail injector. Different injection timings and injection pressures were investigated at two different load points. The mass flow of oxygen was kept constant in order to show how the physical properties (density and temperature) affect the combustion and emission characteristics. The combustion results showed that if the oxygen mass flow is kept constant, EGR is a more efficient way (compared to LIVC) to lower the fuel consumption since it is accompanied with the largest gas flow and thus increased fuel conversion efficiency. The LIVC decreased the fuel consumption at low loads and reduced the emissions at both loads. Transportation of people and goods tend to increase and since internal combustion engines will remain a major power supply for many years to come, reduced fuel consumption is an utmost important way to decrease the CO2 emissions and to move towards a sustainable society. The results in this study show that variable inlet valve timing can be used as one important complementary tool to obtain better combustion characteristics and thus enabling more efficient powertrains.