Passenger cars claim their presence in market by its pick up, top speed and maximum power of the engine. The study described in this paper is focused on improving the low-end performance of a 4-cylinder 1.6 L diesel engine while meeting the targeted maximum power.
To meet the cause turbocharger works as an important element of the engine. A comparative study between regulated two stage turbocharger (R2S) and variable geometry turbocharger (VGT) shows that on a 4-cylinder engine VGT is superior by providing higher boost at 1000 engine rpm full load, than R2S, while in 3-cylinder (same displacement) the opposite effect can be seen. After simulations and iterations, it was confirmed that the in 4-cylinder the exhaust pulse cancellation were leading to a lesser exhaust energy at the turbine inlet. This pulse interaction leads to higher residual gas content which affects the low-end performance.
In continuation with VGT for 4-cylinder engine several iterations were made with different compressor trims to improve the efficiency of the turbocharger which lead to 25% increment in low end torque. Also ported shroud technology is implemented to enhance the surge margin for a better tip in and tip out behavior at vehicle level. The same is further improved by changing the intake suction layout to a D cross section.
To enhance the performance and meet the target torque, exhaust valve timing was modified to reduce the overlap between two consecutive exhaust strokes. This ensures no exhaust pulse interaction and improves the low-end performance. This did not affect much the high-end performance of the engine. The final iteration also helped in significant reduction in smoke at engine level in steady state operation.