With increasingly stringent emission regulations, the cold start emissions have become more important than ever. Using a low compression ratio is a feasible way to improve a heavy-duty engine’s efficiency and emissions. However, cold start performance restricts the development of this technology, especially at high altitudes. In response, we conducted a study of the emissions of a heavy-duty low-compression-ratio diesel engine during start-up process at different altitudes. A plateau simulation system controlled the inlet and exhaust pressure to create altitude environments of 0 m, 1000 m, 2000 m, 3000 m, 3750 m and 4500 m. The gas, particulate and volatile organic compound (VOC) emissions were analyzed with speed and cycle during the start-up process. The results indicated that cold start performance and combustion characteristics became worse as altitudes increased. The gas and particulate emissions of carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbon (THC) and nitrous oxide (NO_X) almost all increased as the engine speed and altitude increased, and was much higher than in idle conditions. The PN and PM emissions in each particle diameter also increased as the altitude increased, which was the same as the nucleation mode and the accumulation mode particles. VOC emissions were also measured, which increased during the start-up process as altitudes increased.

This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine bench test, the effects with the Miller cycle application under 3000 rpm were studied. The results show that the Miller cycle has different extents of improvement on pumping loss, combustion and friction loss. For low, medium and high loads, the brake thermal efficiency of the baseline engine is increased by 2.8%, 2.5% and 2.6%, respectively. Besides, the baseline variable valve timing (VVT) is optimized by the test. Subsequently, the 1D CFD (Computational Fluid Dynamics) model of the Miller cycle engine after the test optimization at the working condition of 3000 rpm and BMEP (Brake Mean Effective Pressure) = 10 bar was established, and the influence of the combined change of intake and exhaust valve timing on Miller cycle was studied by simulation. The results show that as the effect of the Miller cycle deepens, the engine’s knocking tendency decreases, so the ignition timing can be further advanced, and the economy of the engine can be improved. Compared with the brake thermal efficiency of the baseline engine, the final result after simulation optimization is increased from 34.6% to 35.6%, which is an improvement of 2.9%.

This paper presents a study on motor material cost reduction by emphasizing rotor structural advantage in machine performance promotion of a single-phase line-start permanent magnet motor (LSPMM). The cost reduction of LSPMM is focused on saving high-price PM material in the LSPMM design. In the paper, a double-layer interior-PM (IPM) rotor structure is finally adopted to create higher rotor saliency ratio for improving reluctance torque generation to compensate decreased magnet torque due to PM usage reduction. That is, the hybrid torque with higher balance ratio of reluctance toque to magnet torque helps to lower the dependency o PM materials usage. With given torque and efficiency constrains, a series of double-layer rotor structures are built and optimized with gradually reduced amount of PM material. The torque and efficiency performances of LSPMM are predicted by using equivalent circuit method coupled with finite element analysis (FEA). The computed motor torque and efficiency performances are confirmed by comparing with test results.