The demand for a continuous reduction of fuel consumption in today's automotive drives represents a major challenge for industry. Above all, increasing the efficiency of internal combustion engines is of particular importance, along with efficiency-enhancing measures such as hybridization and alternative drive concepts. A promising approach is the realization of an extended expansion stroke in relation to the compression stroke.

The research included the conceptual layout and design of the engine, the thermodynamic and mechanical development, as well as experimental investigations on the fired engine test bench.

Thermodynamic studies demonstrated the need for a variable valve train to improve efficiency over the entire operating range. The expansion stroke of the prototype is approximately twice the compression stroke. Different operating points at full load and at partial load were investigated using different control times and valve lift characteristics. When a valve train with fixed timing is used, the significantly increased efficiency at full load is offset by a moderate partial load efficiency. Variabilities in the valve train, especially with the concept of extended expansion, enable a significant increase in partial load efficiency. The experimental investigations confirmed the simulation results.

In addition to the analysis of the combustion process and charge change in the full load and partial load as well as the influences of the operating behavior on the consumption, the potential of a cylinder switch-off was investigated.

In summary, the Atkinson process implemented via the crank drive kinematics in combination with a variable valve train has a high efficiency potential over the entire operating range.