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The potential of an electric assisted turbocharger for a heavy-duty diesel engine has been analyzed in this work, in order to evaluate the turbo-lag reductions and the fuel consumption savings that could be obtained in an urban bus for different operating conditions. The aim of the research project was to replace the current variable geometry turbine with a fixed geometry turbine, connecting an electric machine which can be operated both as an electric motor and as an electric generator to the turbo shaft. The electric motor can be used to speed up the turbocharger during the acceleration transients and reduce the turbo-lag, while the generator can be used to recover the excess exhaust energy when the engine is operated near the rated speed, in order to produce electrical power that can be used to drive engine auxiliaries. In this way the engine efficiency can be improved and a kind of “electric turbocompounding” can be obtained.

The potential of dual stage turbocharging and Miller Cycle for a six cylinders in line, 13 litres displacement, HD diesel engine was analysed in this work, by means of a 1-D engine simulation fluid dynamic code, coupled with a multi-zone combustion model for NOx and PM prediction. After a detailed validation process, based on an extensive experimental data set, the engine model was then used to predict the effects on engine performance and emission characteristics of different combinations of dual stage turbochargers, engine compression ratio values and intake valve lift profiles. The potential for an appreciable increase in the engine power, with a slight decrease in the specific fuel consumption and a remarkable decrease of NOx specific emissions was demonstrated.

Experimental Design methodologies have been applied in conjunction with objective functions for the optimization of the internal geometry of a rear muffler of a subcompact car equipped with a 1.4 liters displacement s.i. turbocharged engine. The muffler also features an innovative variable geometry design. The definition of an objective function summarising the silencing capability of the muffler has been driving the optimization process with the aim to reduce the tailpipe noise while maintaining acceptable pressure losses and complying with severe space constraints. Design of Experiments techniques for the reduction of experimental plans have been shown to be extremely effective to find out the optimum values of the design parameters, allowing a remarkable reduction of the time required by the design process in comparison with full factorial designs.

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 application of computational methods for the development of a tuned exhaust system for a small two stroke scooter engine has here been evaluated. A single dimension fluid dynamic code has been employed, in order to simulate engine performances at full load with a prototype exhaust system, and data predicted from computer simulation have been compared with experimental results, obtained using a test rig and a data acquisition system specifically designed for small two-stroke engines. In this way the accuracy of the computer model has been assessed not only as far as gross engine performance parameters are concerned, but also concerning the prediction of pressure values in several locations inside the engine and the exhaust system. Finally, computer simulation techniques have been applied to the development of the prototype exhaust system, and have been proved to be powerful and effective techniques to identify the modifications required to obtain the engine performance targets.

The application of computational methods for the development of a high performance four-stroke motorcycle engine has here been evaluated. A single dimension fluid dynamic code has been employed to simulate engine performance at full load, and data predicted from computer simulation have been compared with experimental results. After the abovementioned validation process, computer simulation techniques were applied to develop a variable geometry exhaust system so as to optimize volumetric efficiency over a wider speed range. These techniques proved to be powerful and effective in the identification of the modifications required to obtain the engine performance targets.

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 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.

A new mean value engine model was developed in order to investigate the dynamic performance of vehicles equipped with turbocharged diesel engines, especially as far as the acceleration transients are concerned, where the turbolag phenomenon plays a major role. The turbocharger was modeled through the mass flow and efficiency maps which are usually provided by the manufacturer, with additional extrapolation routines for the map area in the low compression/expansion ratio region, which is particularly important for tip-in manoeuvres simulation. For the internal combustion engine modeling, experimentally derived maps of indicated efficiency, volumetric efficiency and exhaust gas temperature as a function of engine speed and load were used. Finally, a mass balance in the intake and exhaust manifolds was carried out with a filling and emptying technique.

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.

The unsteady flow effects in two different close coupled catalytic converters were investigated in order to achieve a better understanding of the steady state experimental tests which are usually performed to evaluate a flow distribution. Firstly the validity of a CFD model was achieved through a comparison of some steady state simulations with the results of HWA experimental measurements. Several different formulations of the uniformity index, that were found in literature, were then compared, trying to highlight the strengths and shortcomings of each one. Further information was derived from a comparison of the two catalysts that were tested to achieve a general methodology that would be useful for future analysis. Finally, a new approach to evaluate the flow distribution using a steady state analysis was proposed by comparing the results of a transient simulation that was obtained for a whole engine cycle.

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.

Although the use of Exhaust Gas Recirculation (EGR) is nowadays mandatory for automotive diesel engines to achieve NOx emissions levels complying with more and more stringent legislation requirements, electronically controlled EGR systems still represent an expensive technology, often unsuitable for small diesel engines for off-road applications or for two/three wheelers. An interesting option for these categories of small diesel engines is the so-called “internal EGR”, which is obtained by modifying the intake or the exhaust valve lift profile, in order to increase the fraction of exhaust residuals at the end of the intake stroke. Different valve lift profiles were therefore evaluated for a 2 cylinders, 700 cc, Lombardini IDI diesel engine, equipping a light 4 wheelers vehicle.

Numerical simulation can be effectively used to reduce the experimental tests which are nowadays required for the analysis and calibration of engine control systems. In particular in this paper the use of a one-dimensional engine model to analyze the response of an UEGO sensor in the exhaust manifold of a 4 cylinder s.i. engine (with multipoint fuel injection) is described: numerical simulation has been used to simulate a misfunction of the fuelling system, which caused one of the four cylinders to be fuelled with an air/fuel ratio that was 10% richer than the others. The simulated UEGO response was then compared with experimental measurements, and after this validation process, the sensor model can be used to study a proper fuel injection control strategy thus reducing the required experimental tests, as outlined in a test case presented at the end of the paper.

A DoE analysis was carried out to investigate the effects of the compression ratio, injection timing, injector nozzle hole size and number on performance and emissions in a diesel marine engine, aiming to find out the optimal combination between all the abovementioned parameters. The study was performed on a six cylinder in line, 100 liter total displacement, diesel marine engine, by means of a 1-D engine simulation fluid-dynamic code, coupled with a multi-zone combustion model for oxide of nitrogen (NOx) and particulate (PM) prediction. A preliminary detailed validation process, based on an extensive experimental data set, was carried out on the engine model concerning, in particular, the predicted heat release rate, the in-cylinder pressure trace and NOx emissions for several operating points of a propeller load curve.

The application of computational methods for the development of the whole engine-vehicle system has been evaluated in this paper, to highlight the potential of computer simulation techniques applied to the analysis of engine-vehicle matching. First, engine performance was simulated using a one-dimensional fluid dynamic code, and predicted data were compared to experimental results, to assess the accuracy of the engine computer model not only as far as gross engine performance parameters are concerned, but also for the prediction of pressure values at several locations inside the engine. The simulation was also extended to the whole engine operating range, including part-load operating conditions. Afterwards, a vehicle simulation code was employed, to predict vehicle performance and fuel consumption.

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.