Abstract
Heavy-duty diesel engines, the heat engines with the highest thermal efficiency, usually operate under transient conditions. Thus, it is important to study the transient performance of heavy-duty diesel engines. This paper aims to solve the problems of combustion deterioration, poor response, and emission deterioration caused by the mismatch between the air intake response and the fuel system under the strong transient condition of sudden loading of 1 s under constant speed. In this paper, an experimental study on the transient performance at different speeds under the coordinated regulation of a variable geometry turbocharger (VGT) and variable valve timing (VVT) is conducted. The study found that the transient torque response is affected by combustion in the cylinder and pump work. During the low-speed transient process, due to reduced airflow and pumping losses, the VVT is switched off while the VGT delay is increased to improve air response. Consequently, the mixture in the cylinder is fully burned, and improved transient performance is obtained. In the high-speed transient process, the engine air intake flow is improved. Through the VVT is ON at the appropriate time and the VGT hysteresis control, the pumping loss can be effectively reduced, and excellent transient performance can be achieved to ensure the fast response of the in-cylinder charge. Given sudden loading from 10% to 100% within 1 s under a high speed of 1600 r/min, the VVT switches on with a 0.15 s delay, and the VGT is controlled with a 0.4 s delay. A torque response of 0.82 s can be achieved, and the soot peak value is reduced by 66.26%, and the accumulated value of soot is reduced by 46.91%. At a low speed of 1000 r/min, given sudden loading from 10% to 100% within 1 s, the 0.6 s VGT delay can reduce the accumulated value of soot by 78.57% and 56.22% compared with delays of 0.2 and 0.4 s.
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