The Electrified Combustion Engine

Excerpt

Hybrid drives represent the next step in the development of conventional combustion engines, rather than being in competition with them. The electrification of car powertrains is unavoidable if we are to meet the requirements of future legislation on fuel consumption and emissions. All the market studies are forecasting a growing proportion of fully electric drives, but at the same time they are indicating that even by 2030 the majority of vehicles will still have a combustion engine on board. Developing the combustion engine further in the direction of electrification seems to be a sensible solution from both an economic and an environmental perspective. However, electrification will lead to changes in the operating ranges of the combustion engine and the requirements placed on it. Today's combustion engines have to be all-rounders. They need to offer low consumption across all their operating ranges, high low-end torque, and a high power output. This means that in some cases the valve timing and the compression ratio are working against one another. Engine design represents a compromise, unless additional systems are included which make the engine more expensive. Low load levels and low-end torque are less significant in the case of hybrid drives, because the high-torque electric motor is available to provide support or to take over completely. On the other hand, a high level of efficiency over a broad range of engine speeds and loads is of growing importance. Another essential factor is lambda 1 operation across the entire engine map, including full load. Following the introduction of the first generation of the Miller cycle, we will soon see new evolutionary stages of this combustion process. In addition, there will be new developments in fields such as exhaust gas recirculation (HP-EGR and LP-EGR), ignition systems, including pre-chamber spark plugs, high-pressure injection systems with pressures up to 1000 bar, and water injection. All of these offer significant potential for further reducing fuel consumption. Using these measures with combustion engines designed for hybrid drive systems will allow for a two-digit reduction in CO₂ emissions. As a result, hybrid drives will move from being niche products into the mainstream. …