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A variable geometry turbocharger in series with a variable geometry turbocharger (Twin-VGT) system was designed to improve engine power at high altitudes. The influence of altitudes on the performance of the Twin-VGT system was investigated in the perspective of available exhaust energy. The interaction between exhaust flow characteristics of Twin-VGT and openings of Twin-VGT vanes was theoretically analyzed at different altitudes. Meanwhile, a model of a diesel engine matched with the Twin-VGT system was built to study the matching performance of the Twin-VGT system with engine at different altitudes. The optimal opening maps of both high-pressure and low-pressure VGT vanes at high altitudes were obtained to achieve the maximum engine power. The results showed that the optimal openings of high-pressure and low-pressure VGT vanes decreased with increase in altitudes. The operating points of the two-stage compressors located at the high efficiency region and the compressor efficiency region both exceeded 62% at different altitudes. The global expansion ratio increased with increase in altitudes and reached 4.9 at 5500 m. Compared with the VGT in series with a fixed geometry turbocharger on testing bed, exhaust energy of Twin-VGT turbines at low speeds was utilized reasonably and global pressure ratio increased by 0.69–0.94, while brake-specific fuel consumption decreased by 11.24–33.62% under low speeds above altitudes of 2500 m.

In this research, a comparative study of combustion characteristics, performance and emissions of a turbocharged diesel engine fueled with diesel and methanol-Fischer-Tropsch (F-T) diesel-biodiesel-diesel blends at various simulated altitudes (0 m, 3500 m and 5500 m) were conducted. The blends were composed of diesel, methanol, F-T diesel and biodiesel at volume fractions of 65%, 15.2%, 15.6% and 4.2%, respectively. Diesel was used as the baseline fuel, methanol, F-T diesel and biodiesel were used to improve the atomization characteristics, cetane number and stability of the blends, respectively. The results indicated that the cylinder pressure, pressure rise rate and heat release rate of the engine fueled with the blends were lower than those of the diesel at an altitude of 0 m, but higher at an altitude of 5500 m. Peak torque values for the test fuels both appeared at 1400 rpm near the sea level and the speeds corresponding to the peak torque values increased with altitudes. The use of the blends improved the engine power and economic performance at low-speed ranges at an altitude of 3500 m but a dramatically reduce was observed at 5500 m. Compared with the diesel, the particulate matter (2.5 (PM2.5)) for the blends was markedly lower, while a slightly higher in NOx at various altitudes.

To improve engine power at high altitude, the regulated two-stage turbocharger (RTST) which was applied to different altitudes was developed by the authors. The working process model of heavy-duty common-rail diesel engine matched with RTST was built to study the regulating characteristic of variable geometry turbocharger (VGT) vane and both turbine bypass valves and also matching performance of RTST with engine at different altitudes. The control scheme of RTST at different altitudes and engine operating conditions was first put forward, and the optimal opening maps of VGT vane and both turbine bypass valves at different altitudes and engine operating conditions were obtained. The results show that the optimal openings of VGT vane and both turbine bypass valves decrease with increase of altitude, and the optimal opening range of VGT vane becomes narrower with increase of altitude. The operating points of both high-pressure (HP) and low-pressure (LP) compressors locate at high-efficiency region of each compressor map, respectively, and compressor efficiency exceeds 70% at altitude of 5500 m. The total boost pressure ratio increases with altitude and reaches the maximum value of 5.1 at altitude of 5500 m. Compared with single-stage turbocharged engine, the rated power, maximum torque, and torques at lower engine speed at altitude of 5500 m increase by 48.2%, 51%, and 65–121% separately, and the minimum fuel consumption decreases by 12.6%.

The performance of CY4102BZLQ turbocharged diesel engine with the HP60 turbocharger at different high altitudes was studied on the engine test bed for simulating high altitude (low air pressure). The conclusion indicated that the engine performance such as power and economy decreases with the increase of altitude, and the temperature of exhaust increases simultaneously. In addition, the rotational speed of the turbocharger and turbocharger ratio increase with the increase of altitude.

In order to improve the plateau adaptability of CY4102BZLQ-A2A turbocharged diesel engine, the matching performances of the diesel engine with TB28 and HP60 turbochargers at different altitudes (0 m, 2,000 m, 3,000 m, 3,500 m, 4,000 m) were investigated on the engine test bed for simulating high altitude (1ow atmosphere pressure). Results show that HP 60 turbocharger is more suitable to match the engine in terms of engine performance, intake air characteristics, turbocharger rotational speed etc. TB28 turbocharger is over speed when the engine runs at 3,500 m altitude and 2,600 r/min rotational speed, while HP60 turbocharger is over speed when the engine runs at 4,000 m altitude and 2,800 r/min rotational speed. No matter which turbocharger is selected to match the engine, the performance of the engine will deteriorate at different extents. The intake air flow mass and the air-fuel ratio decrease by 7.1-10.5% and 7.2-10.3% respectively with altitude increasing every 1,000 m. By contrast with 0 m altitude, engine torque and power at 4,000 m altitude decrease within 1% and the specific fuel consumption increases by 3.2-3.5% at the maximum torque speed, while the engine torque and power decrease by 4.6-5.3% and 4.5-5.2% respectively and the specific fuel consumption increases by 5.3-11.5% at higher and lower engine rotational speed.