"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 super- charger (ComprexTM) 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 ComprexTM was used in combination with a Miller camshaft. Despite the Miller camshaft, the ComprexTM 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 ComprexTM 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 ComprexTM supercharger. The known drawbacks of the ComprexTM superchargers were solved due to a complete redesign of the machine, which is described in detail.
Keywords: turbocharging; pressure wave supercharging; boosting; low-end torque; Miller valve timing; exhaust aftertreatment; transient operation; exhaust brake; Comprex; water injection
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