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The fuel injection plays a crucial role in determining the mixture formation process in Gasoline Direct Injection (GDI) engines. Pollutant emissions, and soot emissions in particular, as well as phenomena affecting engine reliability, such as oil dilution and injector coking, are deeply influenced by the injection system features, such as injector geometric characteristics (such as injector type, injector position and targeting within the combustion chamber) and operating characteristics (such as injection pressure, injection phasing, etc.). In this paper, a new CFD methodology is presented, allowing a preliminary assessment of the mixture formation quality in terms of expected soot emissions, oil dilution and injector coking risks for different injection systems (such as for instance multihole or swirl injectors) and different injection strategies, from the early stages of a new engine design.

The effect of variations of compression ratio (CR) and injection pressure (IP) on the emissions and performance of a small displacement common rail off-road diesel engine was evaluated. The operating point corresponding to the 5th mode of the ISO 8178 - C1 test cycle (intermediate speed / full load) was considered, since it represents one of the most critical operating conditions as far as exhaust emissions are concerned. The main effect of a reduction of the compression ratio, for a fixed injection timing, was found to be, as expected, an increase in NOx emissions along with a decrease of PM emissions, with a substantial redefinition of the PM-NOx trade-off curve; the choice of a proper value for the start of injection can therefore lead to a better compromise among pollutant emissions, although remarkable variations in BSFC and combustion noise must be taken into account.

Fuel cell vehicles promise to become, in near future, competitive with conventional cars in terms of performance, efficiency and compliance with emission reduction schedules. However, many steps still have to be done, and a series of fundamental choices, such as high vs. low air pressure system options remain unresolved. Modeling can be a powerful instrument to evaluate different components or plant layout, and to predict the dynamic behavior of a fuel cell system. The first part of this paper illustrates the implementation of a direct engineering dynamic model of a load-following fuel cell vehicle. The modeling techniques, assumptions and basic equations are explained for each subsystem, with special attention to the air supply system, whose dynamic simulation was one of the primary targets of this work. Some of the simulation results are presented in the second part.

High pressure common-rail injection systems nowadays allow a very high degree of flexibility in the timing and quantity control of multiple injections, which can be used to obtain significant reductions in engine noise and emissions. The aim of this study is to develop a better understanding of the relationship between injection strategies and the combustion and emission formation process. Some multiple injection strategies (pilot-pilot-main and pilot-main-after) have therefore been analyzed to highlight their influence on soot, NOx, combustion noise and bsfc (brake specific fuel consumption) on a passenger car DI Diesel engine prototype. One operating point (2000×2 rpm/bar) was analyzed for the pilot-pilot-main injection strategy while two operating points (1500×5 and 2500×8 rpm/bar) were tested for the pilot-main-after injection strategy.

The influence of injection pressure on the performance of a FIAT passenger car Diesel engine prototype equipped with a Common Rail Fuel Injection System has been investigated. An increase of the injection pressure from 1300 up to 1500 bar, during this research, has permitted the assessment of the effect of this parameter on the maximum power and on the smoke emissions. The tests were performed at 4000 rpm, with an equal mass of injected fuel. The influence of the injection advance has also been taken into consideration during this experimental analysis. The in-cylinder pressure was first detected and recorded, together with the brake torque and emissions; the in-cylinder pressure was then used for the determination of the principal combustion characteristics, on the basis of the heat release analysis. Finally, higher injection pressure could be used as an effective parameter to increase the maximum power angular speed.