Trading Fuel for Silicon — How Electronics Drive Fuel Efficiency

On the other hand, this also means that still 94% of all light vehicles will run on "classical" combustion engines. And even hybrid cars run the majority of the time on (downsized) gasoline engines. This easily justifies the huge effort taken to improve the fuel efficiency of the engines including their support systems like cooling and fuel supply.

Keeping the fire alive — Direct injection for diesel and gasoline engines

The introduction of high pressure direct injection systems using a "common rail" for fuel distribution at more than 1000 bar was a major milestone in the evolution of diesel engines. The engines got better performance and reduced emissions at a reduced noise level. Solenoid injectors allow three to five injections per cycle, which contributes to a controlled pressure distribution in the cylinder in order to achieve a smoother engine run. Fig.1 shows a simplified power stage of a solenoid type "common rail direct injection" (CRDI) system using "two banks" of injectors. While the injector current is regulated on the high side with switches QH1A to QH2B, the individual cylinder is selected by the low side switches QL1 to QL6. The fast injector opening is enforced by the elevated booster voltage VS2. After activating the injector with QH1A/2A, QH1B/2B are taking over the current switching to VS1 at battery level, which is just high enough to hold the selected injector open. The use of two "banks" of two independent power stages as shown in Fig.1 allows higher flexibility with regard to independent injection timing between the cylinders in order to get higher performance. In compact and mid-size cars, single bank systems are also used to reduce costs.

Figure 1: Generic Power Stage of a Solenoid Type CRDI system - For higher resolution, click here

However, the evolution continues. Replacing solenoid injectors with Piezo technology does have several significant advantages:

Piezo injectors are much faster, resulting in reduced dead times and allowing more accurate control of the injected fuel amount. The fast reaction also allows more injections per cycle (up to 15 and more) reducing rapid pressure changes in the cylinder and nearly eliminating the typical diesel noise.