Comparison of turbocharging and pressure wave supercharging of a natural gas engine for light commercial trucks and vans

Abstract

To increase the efficiency of a natural gas engine, the use of a Miller camshaft was analysed. To avoid a decline in the low-end torque and also in the transient response, a pressure wave supercharger (Comprex™) was compared to the conventional single-stage turbocharger. The analyses for this conceptual comparison were performed experimentally, and the data were then used to run simulations of driving cycles for light commercial vehicles. A torque increase of 49% resulted at 1250 rpm when the Comprex™ was used in combination with a Miller camshaft. Despite the Miller camshaft, the Comprex™ transient response was still faster than the turbocharged engine. Using the same camshaft, the turbocharged engine took 2.5-times as long to reach the same torque. Water injection was used to increase the peak power output while respecting the temperature limitations. As the Comprex™ enables engine braking by design, we show that the use of friction brakes was reduced by two-thirds. Finally, a six-times faster catalyst warmup and an up to 90◦C higher exhaust gas temperature at the three-way catalytic converter added to the benefits of using the Comprex™ supercharger. The known drawbacks of the Comprex™ superchargers were solved due to a complete redesign of the machine, which is described in detail.