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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.

In this study, a new EGR control technique, based on the estimate of the oxygen concentration in the intake manifold, was firstly investigated through numerical simulation and then experimentally tested, both under steady state and transient conditions. The robustness of the new control technique was also tested and compared with that of the conventional EGR control technique by means of both numerical simulation and experimental tests. Substantial reductions of the NOx emissions under transient operating conditions were achieved, and useful knowledge for controlling the EGR flow rate more accurately was obtained.

Different EGR system layouts (a Long Route, a Short Route, and a combination of the two) were evaluated by means of both numerical simulation and experimental tests. In particular, a one-dimensional fluid-dynamic engine model was built in order to evaluate the potential of a Long Route EGR system as well as the potential of different EGR combinations between Long and Short Route. By means of the one-dimensional model, used as a virtual test bench, the estimations of the NOx emissions, based on the Extended Zeldovich Mechanism (EZM), for the different solutions, were compared and valuable information for the calibration of the coordinated EGR LR, EGR SR and Variable Geometry Turbine (VGT) control systems was obtained.

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.

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.

Different diagnostic techniques were experimentally tested on a common rail automotive 4 cylinder diesel engine in order to evaluate their capabilities to fulfill the California Air Resources Board (CARB) requirements concerning the monitoring of fuel injected quantity and timing. First, a comprehensive investigation on the sensitivity of pollutant emissions to fuel injection quantity and timing variations was carried out over 9 different engine operating points, representative of the FTP75 driving cycle: fuel injected quantity and injection timing were varied on a single cylinder at a time, until OBD thresholds were exceeded, while monitoring engine emissions, in-cylinder pressures and instantaneous crankshaft revolution speed.

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.

The loading of a DPF entails the need of trap regeneration by particulate combustion, whose efficiency and frequency are somehow affected by the way soot is deposited along the channels. The aim of this work is therefore the development of a new experimental methodology able to provide fundamental information about the soot loading process inside the DPF, in order to take advantage of this insight for DPF design and optimization purposes. Small lab-scale 300 cpsi DPF samples were loaded downstream of the DOC in an ad hoc designed reactor capable of hosting 5 samples, by diverting part of the entire flow produced by an automotive diesel engine at 2500 rpm × 8 BMEP, selected as representative of the most critical operating conditions for soot production during the New European Driving Cycle (NEDC).

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 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 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.

An experimental investigation was carried out in order to point out the state of the art of the exhaust emissions of small spark ignition engines for non-road mobile machinery. 14 different engines from different manufacturers, with rated power below 18 kW, were selected as representative of the most common non-road mobile machinery, including lawn mowers, chain saws, trimmers, snow-removal equipments and portable gensets: 10 engines were 4-stroke (one of which also equipped with a three-way catalyst), while 4 were 2-stroke (three of which equipped with an oxidation catalyst). After a run-in period, exhaust emissions were measured according to different test cycles: moreover, an endurance run test of 100 hours was also performed for 5 engines.

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 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 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.

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.

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.

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.