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The development of a leanburn engine is described, in which optimized engine design, innovative engine management and exhaust gas aftertreatment using a special NOx-storage catalyst were combined to yield a significant improvement in fuel economy with reduced NOx emissions. To achieve stable combustion near the lean limit a swirl system was used and the appropriate parameters of the 2.2 I 4-cyIinder 4-valve SI engine were optimized. As a result, the mixture formation was improved and the lean limit was extended to higher air-fuel ratios. An adaptive lambda controller which was based on the evaluation of engine-smoothness calculated from the RPM-sensor was implemented to control each cylinder individually close to the lean limit. A model-based control system was developed to achieve extremely accurate air-fuel ratio control during transients.

In conjunction with throttle-free load control on a 4-valve, single-cylinder spark-ignition engine, the influencing variables of charge cycle, mixture formation and combustion process are presented both as computer calculations and on the basis of test results. The influences of the position of the maximum of the inlet valve stroke, the position of the inlet close, the shape of the valve stroke and the load motion in relation to the maximum power and minimum fuel consumption are investigated in full load by computer calculations and in partial load by engine tests.

A detailed, one-dimensional, time dependend model is presented, describing flame kernel development in spark ignition engines which explicitely accounts for all fundamental properties of the ignition system (supplied electrical energy and power, discharge mode, energy transfer efficiency to spark plasma, plasma temperature distribution, gap width, heat losses to electrodes and chamber walls), of the combustible mixture (pressure, temperature, equivalence ratio, residual gas fraction, laminar burning velocity, type of fuel) and of the flow field (mean flow velocity, turbulence intensity, strain, characteristic time and length scales, flame holder effects). The model is based on the strained flamelet model and predicts kernel growth consistently under virtual all relevant physical/chemical conditions. Model predictions have been verified in extensive studies in an optical engine over a wide range of physical/chemical parameters using advanced optical and laser optical diagnostics.

Realization of the leanburn SI engine's potential for improved fuel economy strongly depends on precise control of the air-fuel ratio (AFR), especially during transients, for acceptable driveability and low exhaust emissions. The development of an adaptive-feedforward model-based AFR controller is described. A discrete, nonlinear, control-oriented engine model was developed and used in the AFR control algorithm. The engine model includes intake-manifold airflow dynamics, fuel wall-wetting dynamics, process delays inherent in the four-stroke engine cycle, and exhaust-gas oxygen (UEGO) sensor dynamics. The sampling period is synchronous with crank-angle (“event-based”) for more precise control. The controller relies on the engine speed and throttle position for load information. An intake-manifold pressure (MAP) sensor is used for identification of the airflow dynamics, but not for control. The MAP sensor would also be useful for the cold start and for engine diagnostics.

For development of new engines a ‘general purpose ECU’ for spark ignition engines with up to 12 cylinders has been developed. As part of this ECU a DSP (Digital Signal Processor)-based measurement unit for high frequency combustion analysis has been integrated. In this paper, details about this signal processing platform are given. The DSP-unit has 24 analog input channels. 12 channels are used for cylinder pressure measurement; the other 12 channels are general purpose ones. For example, they can be used for ionic current analysis. Additional digital inputs allow measurement of crank speed and crank speed variations. This is an important topic for misfire detection as part of the OBD regulations.

Pilot injection gas engines are commonly used as large stationary engines. Often, the combustion is implemented as a dual-fuel strategy, which allows both mixed and diesel-only operation, based on a diesel engine architecture. The current research project focuses on the application of pilot injection in an engine based on gasoline components of the passenger car segment, which are more cost-effective than diesel components. The investigated strategy does not aim for a diesel-only combustion, hence only small liquid quantities are used for the main purpose of providing a strong, reliable ignition source for the natural gas charge. This approach is mainly driven to provide a reliable alternative to the high spark ignition energies required for high cylinder charge densities. When using such small liquid quantities, a standard common-rail diesel nozzle will apparently not be ideal regarding some general specifications.

Synthetic fuels for internal combustion engines offer CO2-neutral mobility if produced in a closed carbon cycle using renewable energies. C1-based synthetic fuels can offer high knock resistance as well as soot free combustion due to their molecular structure containing oxygen and no direct C-C bonds. Such fuels as, for example, dimethyl carbonate (DMC) and methyl formate (MeFo) have great potential to replace gasoline in spark-ignition (SI) engines. In this study, a mixture of 65% DMC and 35% MeFo (C65F35) was used in a single-cylinder research engine to determine friction losses in the piston group using the floating-liner method. The results were benchmarked against gasoline (G100). Compared to gasoline, the density of C65F35 is almost 40% higher, but its mass-based lower heating value (LHV) is 2.8 times lower. Hence, more fuel must be injected to reach the same engine load as in a conventional gasoline engine, leading to an increased cooling effect.