In the 1980s, Comprex superchargers were used in diesel passenger cars by Opel and Mazda. But the supercharger had drawbacks: During cold starts, it was difficult to build up the pressure wave process, and temperature-related effects during load changes led to higher emissions and efficiency problems.

Meanwhile, engineers from the Swiss company Antrova AG have further developed the Comprex supercharger: Supported by an electric motor, it works smoothly in all conditions, and a new design of the so-called cell rotor completely solves the difficulties caused by temperature changes. Empa researchers, in collaboration with a commercial vehicle manufacturer and the Comprex manufacturer, have built a natural gas engine with such a "Comprex 2.0" supercharger and have been able to demonstrate that the new Comprex design works perfectly well in cold start conditions as well as under warm and dynamic operation. In contrast to its turbo counterpart, the engine delivers enormously high torque practically from idle speed, which on the one hand improves drivability and, in combination with so-called Miller operation and an adjustment of the transmission ratio, helps save fuel.

At the same time, the catalytic converter warms up six times faster than in a turbocharged engine, which ensures better exhaust gas values. Finally, the Comprex enables a high engine braking effect – truck drivers would have to use the mechanical brakes much less frequently.

In Empa's engine laboratory, the Comprex supercharger was tested in conjunction with a gas engine. Image: Empa