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The End of Compromise
Published in Patrick Hossay, Automotive Innovation, 2019
A more elegant solution comes from the possibility of a variable geometry turbocharger. Variable geometry turbos (VGT) have been used to improve low-end engine torque in diesel engines for a couple of decade, but this technology was not available to gasoline engines because of the significantly higher exhaust temperatures of gas engines. Manufacturing a variable mechanism that could withstand the high temperatures of a gasoline exhaust system simply wasn’t possible. But recent advances in material technology have changed this. A VGT can vary the effective geometry of the turbine, typically with movable vanes, and thus adjust the turbine for quick spool up or high boost throughout the engine speed range. The result is a high total boost capability, with imperceptible turbo lag (Image 2.14).
Optimization of diesel engine dual-variable geometry turbocharger regulated two-stage turbocharging system based on radial basis function neural network-quantum genetic algorithm
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Guangmeng Zhou, Ruilin Liu, Zhongjie Zhang, Chunhao Yang, Haojian Ding
The RTST system has the working characteristics of high-pressure ratio and wide flow, which plays an important role in improving the performance of diesel engines under high-altitude conditions. The VGT improves the exhaust gas expansion ratio by reducing the effective flow area of the turbine. It has better regulation and turbocharger efficiency (Yang et al. 2018; Zhang, Liu, and Lin et al. 2019), and can significantly improve the transient response of diesel engines under high-altitude conditions. Combining VGT technology with the RTST system enables diesel engine to more reasonably and effectively use exhaust energy and control intake air flow under different altitude conditions. However, the introduction of VGT makes the diesel engine turbocharging system more complicated, and the calibrated turbocharging parameters at a fixed altitude may not be suitable for other altitude environments. Therefore, it is necessary to carry out the optimization study of different altitude parameters of the diesel engine dual-VGT RTST system.
Study on prediction model of diesel engine with regulated two-stage turbocharging system based on hybrid genetic algorithm-particle swarm optimization method at different altitudes
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Ruilin Liu, Haojian Ding, Zhongjie Zhang, Chunhao Yang, Guangmeng Zhou
Figure 3 illustrates the variation curve of intake flow and boost pressure. It can be seen from the figure that under the conditions of fixed altitude and variable speed, the diesel engine HP and LP stage pressure ratio increases with the increase in the speed at the low- and medium-speed conditions. In the middle- and high-speed conditions, the LP stage pressure ratio increases with the speed increase, and the HP stage pressure ratio decreases with the speed increase. This is due to the fact that in order to prevent the mechanical load of the diesel engine from being too high at high speeds, the variable geometric turbocharger (VGT) blade opening of the HP stage increases, resulting in a decrease in the expansion work of the HP stage turbine and a reduction in the pressure ratio of the HT. When the fixed-speed changes to altitude, the HP and LP pressure ratios show different trends at different speeds as the altitude increases. The change of HP stage pressure ratio is related to the VGT blade opening. When the VGT blade opening decreases, the turbine flow cross-section decreases, the vortex front pressure and the adiabatic jet expansion work of the turbine increase, and eventually the turbocharger pressure ratio increases. The LP stage pressure ratio decreases with the increase in altitude at low speeds. This is due to the decrease in diesel engine fuel injection with lower altitude, lower exhaust energy and turbine expansion work, and the compressor even idles at 5,500-m altitude. The exhaust energy of the diesel engine is sufficient at medium and high speeds. Due to the low exhaust pressure of the LP turbocharger at high altitudes, the high-altitude pressure ratio is greater than the plain pressure ratio.