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At high altitude and low pressure, the changes of inlet and exhaust pressure and the combustion environment in the cylinder lead to the deterioration of physicochemical characteristics and combustion in the cylinder of the coal-based mixed fuel. In this research, based on the plateau environment simulation test platform, the combustion characteristics, dynamic performance and fuel economy of the turbocharged diesel engine burned at different simulated altitudes (0 m, 1500 m, 2500 m, 3500 m and 4500 m) were studied. The results revealed that as altitude increased, the coal-based composite fuel caused the diesel engine's in-cylinder pressure, pressure rise rate, and instantaneous heat release rate to gradually decrease, the flameout period to gradually extend, and the center of gravity of combustion to gradually delay. At low engine speed, the average effective pressure cycle variation rate increased significantly. The coal-based complex fuel diesel engine has increased in-cylinder pressure, torque, and effective thermal efficiency, as well as peak instantaneous heat release rate at high altitude, when compared to diesel combustion. It also causes a reduction in the maximum pressure rise rate, a forward shift in the combustion center of gravity, a reduction in the average effective pressure cycle rate of change, and a shortening of the stall period. [ABSTRACT FROM AUTHOR]

The decrease of inlet charge and mismatch of air and fuel are main reasons for the decrease of engine performance at variable altitudes. Understanding coupling mechanism between two-stage turbocharging and fuel injection system is key to maximize its potential for engine power recovery at variable altitudes. This paper focused on the coupling characteristic of twin variable geometry turbocharging (Twin-VGT) and fuel injection parameters on key parameters of gas path, in-cylinder combustion, and energy flow of the diesel engine at variable altitudes. Firstly, a thermodynamic cycle model of a Twin-VGT diesel engine aiming at variable altitudes was established and validated by experimental data. Furthermore, the coupling mechanism of high-pressure variable geometry turbocharging (HVGT) and low-pressure variable geometry turbocharging (LVGT) vanes on exhaust available energy (EAE), global expansion ratio (GER) and its distribution, global boost ratio (GBR) and its distribution, isentropic efficiency of the Twin-VGT, combustion process, and energy flow of the engine were studied at different altitudes. Enthalpy drop ratio is regulated by HVGT and LVGT and the isentropic efficiency of two-stage turbine reaches to maximum when openings of HVGT and LVGT at 0.35 and 0.75, respectively, at the altitude of 5500 m. Finally, this paper investigated the coupling characteristic of turbocharging and fuel injection parameters on combustion process and engine performance, which provides the theoretical basis for collaborative controlling of the Twin-VGT and fuel injection parameters at variable altitudes. Brake thermal efficiency (BTE) is affected by exhaust temperature which is mainly controlled by HVGT openings and injection advance angle (IAA) at variable altitudes, and BTE reaches to maximum when openings of HVGT at 0.4 and IAA at −5.5°CA under fixed engine load at the altitude of 5500 m. [ABSTRACT FROM AUTHOR]

Increasingly complex air path concepts are investigated to achieve improving the power while reducing fuel consumption of diesel engines at high altitudes. One promising technology is the Twin-VGT (variable geometry turbocharger) for diesel engines. A control concept has to be developed to exploit boost potential by coordinated management of the two turbocharger stages at different altitudes. In this paper, a nonlinear model prediction control (NMPC) algorithm based on back propagation neural network (BPNN) was proposed to purpose multi-parameter control of turbocharging system at high altitudes. Optimal control sequences of NMPC were solved by improved particle swarm optimization (PSO), and boost pressure and intake flow achieved good dynamic tracking performance by collaborative control high-pressure VGT (HVGT) and low-pressure VGT (LVGT) under whole operative conditions at high altitudes. NMPC achieved better step response performance compared with PID controller at different altitudes. NMPC control error of intake flow and boost pressure are within 0.26% under steady and transient conditions, exhibiting higher control accuracy and responsiveness even under transient operating conditions at high altitudes. [ABSTRACT FROM AUTHOR]