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Fuel consumption and NOx emissions of different Diesel-Electric hybrid powertrains, equipping a midsize European passenger car were evaluated in this paper through numerical simulation. Different degrees of hybridizations, from micro to mild hybrids, and different architectures and power sources management strategies were taken into account, in order to obtain a preliminary assessment of the potentialities of a Diesel-Electric hybrid system for the European passenger car market. Both regulated driving cycles, such as NEDC, and “real-world representative” driving cycles, such as Artemis cycles, were evaluated, in order to obtain not only an estimate of the impact of hybridization on type-approval CO2 and NOx emissions, but also an assessment of the impact of these technologies from the vehicle owner's perspective. Finally, the effects of internal combustion engine downsizing was also considered.

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.

Different hybrid powertrains for a European mid-size passenger car were evaluated in this paper through numerical simulation. Different degrees of hybridizations, from micro to mild hybrids, and different architectures and power sources management strategies were taken into account, in order to obtain a preliminary assessment of the potentialities of different hybrid systems for the European passenger car market. Both diesel and gasoline internal combustion engines were considered: a 1.6 dm₃ Common Rail turbocharged diesel, and a 1.4 dm₃ spark ignition turbocharged engine, equipped with an innovative Variable Valve Actuation system. Diesel hybrid powertrains, although being subject to NOx emissions constraints that could jeopardize their benefits, offered substantial advantages in comparison with gasoline hybrid powertrains. Potentialities for fuel consumption reductions up to 25% over the NEDC were highlighted, approaching the 2020 EU 95 g/km CO₂ target.

Design of Experiments (DoE) methodologies have been applied in conjunction with objective functions to the experimental optimization of multiple injection strategies for a small displacement Common Rail (CR) off-road diesel engine. One operating point, which corresponds to the 5th mode of the ISO 8178 - C1 test cycle (intermediate speed / full load), was considered during this analysis: this operating condition is one of the most critical as far as exhaust emissions for the considered engine are concerned. Three injections were actuated per engine cycle during the experimental tests, with different strategies characterized by different timings and durations of each injection. It was found that DoE techniques for the reduction of experimental plans can be very effective in finding the optimum values for the injection parameters, leading to a remarkable reduction in the calibration process time, compared to full factorial designs.

The influence of pilot injection timing and quantity on soot, NOx, combustion noise and bsfc has been analyzed on a passenger car DI Diesel engine prototype equipped with a common rail fuel injection system. The investigated engine operating points were 1500/5, 2000/2, 2500/8 rpm/bar, which are quite typical of EC driving cycles. For each of these operating conditions, the pilot injection quantity was varied by up to 15% of the total injected quantity and the pilot injection timing was varied between 32° and 1° crank angle degrees. The principal combustion characteristics were determined on the basis of the heat release, and a thorough statistical analysis was performed to infer the correlation between the combustion parameters and soot and NOx emissions.

The influence of different multiple injection strategies on the emissions, combustion noise and BSFC (brake specific fuel consumption) of a small non-road diesel engine prototype equipped with a Common Rail (CR) fuel injection system has been analysed. The two most critical operating points according to the ISO 8178 - C1 test cycle as far as the exhaust emissions are concerned (Intermediate Speed/Full Load; Rated Speed/Full Load) were considered. Different injection strategies, each with a fixed number of consecutive injections (up to 4), were tested for the selected operating points. It was found that multiple injection strategies can be very effective also for small displacement non-road diesel engines in reducing particulate matter (PM), NOx and noise levels without increasing fuel consumption.

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 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.

Gasoline direct injection in two-stroke engines has led to even more advantageous results, in comparison with four-stroke engines, as far as unburned hydrocarbon emissions and fuel consumption are concerned. A new electronically controlled injection system has therefore been fitted in a crankcase-scavenged two-stroke engine, previously set up with indirect injection equipment. The comparison between the performance of the two gasoline feeding systems has highlighted the potential of the direct injection strategy. The direct injection system here tested has allowed the optimization of the engine torque characteristic at wide open throttle operating conditions. Moreover, the engine original exhaust system, has been replaced with an expansion-chamber exhaust-pipe system, in order to evaluate the impact of direct gasoline injection also with these optimized exhaust configuration.