Marc Sens

Gasoline engine simulations using zero-dimensional spark ignition stochastic reactor model and three-dimensional computational fluid dynamics engine model

A simulation process for spark ignition gasoline engines is proposed. The process is based on a zero-dimensional spark ignition stochastic reactor model and three-dimensional computational fluid dynamics of the cold in-cylinder flow. The cold flow simulations are carried out to analyse changes in the turbulent kinetic energy and its dissipation. From this analysis, the volume-averaged turbulent mixing time can be estimated that is a main input parameter for the spark ignition stochastic reactor model. The spark ignition stochastic reactor model is used to simulate combustion progress and to analyse auto-ignition tendency in the end-gas zone based on the detailed reaction kinetics. The presented engineering process bridges the gap between three-dimensional and zero-dimensional models and is applicable to various engine concepts, such as, port-injected and direct injection engines, with single and multiple spark plug technology. The modelling enables predicting combustion effects and estimating the risk of knock occurrence at different operating points or new engine concepts for which limited experimental data are available.

Ignition Systems for Gasoline Engines

In addition to increasing electrifi cation, forecasts show a worldwide increase in the number of gasoline engines being produced. Rising industrialization will likely lead to 120 million new registrations, at least 75% of them for vehicles based on combustion engines, by the year 2030. Ambitious climate targets will remain a chimera as long as the gasoline engine is not adapted to help significantly reduce carbon emissions. In addition to the requirements of the established markets, we must be prepared for new challenges in emerging economic regions in particular. Engines require greater optimization while remaining sufficiently robust to meet the demands of use all around the world. In addition to the Miller combustion cycle, the industry needs engines that employ strongly chargediluted combustion to achieve efficiencies significantly above 40%. Instrumental in this will be ignition processes with great potential to shift ignition limits.

Selecting a suitable stroke / bore ratio when combining variable compression and Early Intake Valve Closure (EIVC)

Increasingly strict fuel consumption and emission legislation is forcing engine developers to use combinations of technologies that complement each other to produce high potential for cutting fuel combustion.

Simulation of the Effects of Spark Timing and External EGR on Gasoline Combustion Under Knock-Limited Operation at High Speed and Load

Combustion in a spark ignition engine operated at high speed and load is investigated numerically with regard to knock behavior. The study focuses on the concurrent impact of spark timing and exhaust gas recirculation (EGR) on the severity of knock. Specifically, the possibility of knock reduction through the lowering of nitrogen oxide (NO) content in the rest-gas is examined. Simulations are carried out using a stochastic reactor model of engine in-cylinder processes along with a quasi-dimensional turbulent flame propagation model and multicomponent gas-phase chemistry as gasoline surrogate. The knock-limited conditions are detected using the detonation diagram. By lowering the NO content in the external EGR the end-gas auto-ignition is suppressed. This prevents a transition to knocking combustion and enables advancing of spark timing that yields better combustion phasing. As a result, fuel economy is improved and the potential benefits of cleaning the EGR are indicated.

Gasoline Heated Fuel Injection – A Mechanism for Particulate Reduction and General GDI Engine Optimization

Mixture formation in gasoline direct-injection engines is mainly determined by the interaction of air motion and fuel injection spray quality. Injection systems with a wide range of designs are being developed for enhanced spray and mixture quality. The optimization of mixture preparation quality is targeted at increasing the combustion efficiency and at reducing exhaust gas pollutants, especially soot formation and the associated particle number emission. The pressure and temperature of injected fuel play a crucial part in defining spray quality; the effect of increasing injection pressure has on spray quality is basically known. The positive effect that increasing injected fuel temperature has on spray quality and on engine emission has been reported, however, the underlying mechanisms are complex and not well understood. Based on the first promising results from single cylinder SI engine tests a collaborative research project was initiated focusing on the impact of the injection of heated fuel on engine operation. An injector capable of injecting gasoline up to the supercritical condition was designed for installation in a single cylinder research engine. The injector is capable of being operated with fuel temperatures of up to 350°C and fuel pressures up to 300 bar, thus allowing the impact of different fuel temperatures and pressures on the spray formation, combustion process and exhaust pollutants under various engine conditions to be investigated. The paper presents heated fuel spray characterization, spray modeling in CFD and engine test data to show the impact of heated fuel on spray formation and exhaust emissions with spark ignited engine operation. The results from the collaborative project will include high speed spray photography, droplet size measurement, spray modeling in supercritical, vapor and liquid phases for pressure vessel and engine in-cylinder conditions, engine exhaust emissions and optical in-cylinder spray visualization using video endoscopy measurements. The interaction of heated fuel injection with engine variable valve lift and timing operation will also be presented.

Aufladung von Verbrennungsmotoren

In den vorausgegangenen Kapiteln wurden die wichtigen Ziele bei der Entwicklung von Verbrennungsmotoren, namlich guter Wirkungsgrad, das heist niedriger Kraftstoffverbrauch und niedrige Emissionen, ausfuhrlich dargestellt. Ein weiterer wichtiger Punkt ist die Erhohung der Leistungskonzentration eines Verbrennungsmotors. Es geht also darum, aus einem definierten Bauvolumen oder/und aus einem vorgegebenen Motorgewicht moglichst viel Leistung zu gewinnen. Die Erhohung der Leistungskonzentration ist unter Umstanden zusatzlich mit einer Wirkungsgradverbesserung verbunden.