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The introduction of new light-duty vehicle emission limits to comply under real driving conditions (RDE) is pushing the diesel engine manufacturers to identify and improve the technologies and strategies for further emission reduction. The latest technology advancements on the after-treatment systems have permitted to achieve very low emission conformity factors over the RDE, and therefore, the biggest challenge of the diesel engine development is maintaining its competitiveness in the trade-off "CO2-system cost" in comparison to other propulsion systems. In this regard, diesel engines can continue to play an important role, in the short-medium term, to enable cost-effective compliance of CO2-fleet emission targets, either in conventional or hybrid propulsion systems configuration. This is especially true for large-size cars, SUVs and light commercial vehicles. In this framework, a comprehensive approach covering the whole powertrain is of primary importance in order to simultaneously meet the performance, efficiency, noise and emission targets, and therefore, further development of the combustion system design and injection system represent important levers for additional improvements. For this purpose, a dedicated 0.5 dm3 single-cylinder engine has been developed and equipped with, a state-of-the-art Euro 6 combustion system, and an advanced common rail fuel injection system (FIS) offering higher flexibility in terms of injection strategy and higher quantity accuracy. Three injector nozzles with different hydraulic flow rates (HF) have been selected and employed for the overall combustion process optimization. The optimization has been performed by means of an extensive DoE-based test campaign in which the engine and FIS operating parameters have been parametrized with the aim to carry out a proper combination in terms of HF and injection strategy. The results at partial load conditions evidence significant advantages in applying an advanced injection pattern, while the HF reduction can significantly improve the smoke emission and combustion noise without fuel consumption penalties. Therefore, a proper combination and optimization of the HF and injection strategy can provide low noise and engine-out smoke while maintaining the rated power performance targets.

Diesel will continue to be an indispensable energy carrier for the car fleet CO2 emission targets in the short-term. This is particularly relevant for heavy-duty vehicles as for mid-size cars and SUVs. Looking at the latest technology achievements on the after-treatment systems, it can be stated that the concerning about the NOx emission gap between homologation test and real road use is basically solved, while the future challenge for diesel survival is to keep its competitiveness in the CO2 vs cost equation in comparison to other propulsion systems. The development of the combustion system design still represents an important leverage for further efficiency and emissions improvements while keeping the current excellent performance in terms of power density and low-end torque. The paper describes the results achieved in developing a new diesel combustion system for car application that, leveraging on the high flexibility of the latest fuel injection technology, combines outstanding power and fuel efficiency with low pollutant emissions in ultralight engine designed for lower maximum peak cylinder pressure. The study has been carried out on a 0.5l single-cylinder engine on which an advanced and last generation common rail system, capable of very high injection pressure, has been installed. Through an extensive DoE-based test campaign in which all engine operating parameters have been carefully parametrized, the capability to achieve high power density and excellent fuel economy with low engine-out pollutant emissions has been demonstrated and discussed in the paper.

[EN] This article describes the main results of an investigation about counter-bore injector nozzle impact on the combustion process in a modern Euro 6 diesel engine. First, hydraulic and spray visualization tests have been performed, showing a potential advantage of such nozzle design in fuel-air mixing efficiency. Then, combustion performance has been assessed on a GM-designed 1.6-L four-cylinder engine. The engine has been installed on a dynamometric test bench and instrumented with an AVL cylinder pressure transducer for heat release rate analysis, as well as HORIBA MEXA gas analyzer for exhaust emissions and AVL 415 Smoke Meter. Engine efficiency and emissions have been analyzed on four different part-load steady-state points, representative of New European Driving Cycle and Worldwide harmonized Light duty Test Cycle certification cycles, and covering engine speeds from 1250 to 2000 r/min and brake mean effective pressure between 0.2 and 1.4 MPa. Results of indicated analysis show that counter-bore nozzles have significant differences in terms of pilot injection combustion at low load points, which in turn lead to a better ignition and shorter combustion of the main injection. In addition, an improvement of diffusive combustion is observed as load increases. Because of both, fuel consumption is reduced by approximately 1% with respect to a standard nozzle. Finally, an appreciable decrease in engine exhaust emissions has been recorded, especially in terms of particulate matter and hydrocarbon emissions. This reduction has been linked to the improvement of fuel-air mixing promoted by the counter-bore nozzle previously observed., The authors would like to thank General Motors Global Propulsion Systems-Torino S.r.l. for sponsoring the current work. Part of the equipment was purchased with the help of Generalitat Valenciana in project IDIFEDER2018 with title "Equipamiento de diagnostico optico de alta velocidad para estudiar procesos de inyeccion''.

The paper describes the results achieved in developing a new diesel combustion system for passenger car application that, while capable of high power density, delivers excellent fuel economy through a combination of mechanical and thermodynamic efficiencies improvement. The project stemmed from the idea that, by leveraging the high fuel injection pressure of last generation common rail systems, it is possible to reduce the engine peak firing pressure (pfp) with great benefits on reciprocating and rotating components light-weighting and friction for high-speed light-duty engines, while keeping the power density at competitive levels. To this aim, an advanced injection system concept capable of injection pressure greater than 2500 bar was coupled to a prototype engine featuring newly developed combustion system. Then, the matching among these features have been thoroughly experimentally examined. The results confirmed the benefits of the employment of high fuel injection pressures as a way to reduce the pfp, combining competitive performance and excellent fuel efficiency with emissions and Noise Vibration Harshness (NVH) requirements of last generation diesel engines for passenger car applications. In particular, the paper discusses the engine power and efficiency sensitivities to the boundary conditions of the charging/exhaust systems, the fuel injection pressure and the mechanical base engine design (with particular reference to the pfp). Eventually, a balanced set of targets for the entire system based on such results are carried out.

The paper describes the challenges and results achieved in developing a new high-speed Diesel combustion system capable of exceeding the imaginative threshold of 100 kW/l. High-performance, state-of-art prototype components from automotive diesel technology were provided in order to set-up a single-cylinder research engine demonstrator. Key design parameters were identified in terms boost, engine speed, fuel injection pressure and injector nozzle flow rates. In this regard, an advanced piezo injection system capable of 3000 bar of maximum injection pressure was selected, coupled to a robust base engine featuring ?-shaped combustion bowl and low swirl intake ports. The matching among the above-described elements has been thoroughly examined and experimentally parameterized. The tests confirmed the benefits of the employment of very high fuel injection pressures as a way to decouple the trade-off between an excellent power rating and emissions / NVH / CO2 at part load, whose combination truly defines the leading edge of modern diesel engines for automotive application. The paper also discusses the system sensitivity to the boundary conditions, of the charging and exhaust systems, and develops a balanced set of targets for the entire system based on thermo-structural, fluid-dynamics and efficiency considerations. This would represent, in the authors' view, the 'recipe' for the next generation of premium diesel engines for automotive application

The integration of the exhaust manifold in the engine cylinder head has received considerable attention in recent years for automotive gasoline engines, due to the proven benefits in: engine weight diminution, cost saving, reduced power enrichment, quicker engine and aftertreatment warm-up, improved packaging and simplification of the turbocharger installation. This design practice is still largely unknown in diesel engines because of the greater difficulties, caused by the more complex cylinder head layout, and the expected lower benefits, due to the absence of high-load enrichment. However, the need for improved engine thermomanagement and a quicker catalytic converter warm-up in efficient Euro 6 diesel engines is posing new challenges that an integrated exhaust manifold architecture could effectively address. A recently developed General Motors 1.6L Euro 6 diesel engine has been modified so that the intake and exhaust manifolds are integrated in the cylinder head. Extensive CAD/CAE/CAM analyses have been employed in order to guide the design of the overall surface and the water cooling jacket that surround the exhaust manifold of the new engine version, and thus to be able to improve the low-frequency thermal fatigue resistance of the head. The thus obtained prototype engine head has been tested on a highly-dynamic test bench at the Politecnico di Torino in order to characterize performance, emissions and thermal behavior in comparison to the baseline production engine. The results have generally been very promising and have shown the possibility of maintaining the same performance rating over the overall engine speed range as well as comparable emissions and brake specific fuel consumption in steady-state conditions. Furthermore, appreciably faster engine and aftertreatment warm-up have been recorded due to the higher heat fraction that is transferred to the coolant and to the more favorable exhaust gas enthalpy management. The latter benefit is in fact very interesting as far as the control of HC and CO emissions within the NEDC homologation is concerned

The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the capability of GM Combustion Closed-Loop Control (CLCC) in enabling seamless operation with high biodiesel blending levels in a modern diesel engine for passenger car applications. As a matter of fact, fuelling modern electronically-controlled diesel engines with high blends of biodiesel leads to a performance reduction of about 12-15% at rated power and up to 30% in the low-end torque, while increasing significantly the engine-out NOx emissions. These effects are both due to the interaction of the biodiesel properties with the control logic of the electronic control unit, which is calibrated for diesel operation. However, as the authors previously demonstrated, if engine calibration is re-tuned for biodiesel fuelling, the above mentioned drawbacks can be compensated and the biodiesel environmental inner qualities can be fully deployed. In order to enable such calibration re-tuning, it is fundamental to achieve a reliable biodiesel blending detection, and to use it for realtime combustion optimization, chiefly by optimizing the injection train. Therefore, the authors investigated the capability of CLCC to detect biodiesel blending ratio on the recently released 2.0L Euro5 GM diesel engine equipped with embedded pressure sensors in the glow plugs. Various blends of biodiesel were tested, notably 20% by volume (B20), 50% (B50) and pure biodiesel (B100). Tests on the multicylinder engine were carried out in a wide range of engine operating points for the complete characterization of the biodiesel performance in the NEDC cycle. The results demonstrated the successful capability of the CLCC control to detect biodiesel blending with reasonable accuracy and to implement the corrective actions to avoid emission drift and performance losses.

Biofuel usage is increasingly expanding thanks to its significant contribution to a well-to-wheel (WTW) reduction of greenhouse gas (GHG) emissions. In addition, stringent emission standards make mandatory the use of Diesel Particulate Filter (DPF) for the particulate emissions control. The different physical properties and chemical composition of biofuels impact the overall engine behaviour. In particular, the PM emissions and the related DPF regeneration strategy are clearly affected by biofuel usage due mainly to its higher oxygen content and lower low heating value (LHV). More specifically, the PM emissions and the related DPF regeneration strategy are clearly affected by biofuel usage due mainly to its higher oxygen content and lower low heating value, respectively. The particle emissions, in fact, are lower mainly because of the higher oxygen content. Subsequently less frequent regenerations are required. On the other hand, as a consequence of the lower LHV of the RME, a larger amount of post - injected fuel is required for the achievement of the right temperature inside the DPF for the oxidation of the soot cake. This could generally result in to a larger oil dilution, a higher smoking and an increment of fuel consumption. Aim of the paper is the characterization of the particle emissions in terms of mass, size and number during the regeneration of a Close Coupled DPF (CCDPF). The measurements were performed at the exhaust of a 2.0l Euro5 CR GM Diesel engine fuelled both with conventional diesel fuel (RF) and Rapeseed Methyl Ester (RME). The investigation was carried out at a steady state engine operating point (2750rpm 12bar BMEP) representative of a typical extraurban driving condition. The regeneration was performed using an actual regeneration strategy adopted in the last generation diesel engine for RF and a modified one for RME. The particulate emissions were characterized by means of a microsoot sensor, for the mass concentration measurement, and a DMS500, for the particle sizing and counting. The results pointed out the benefit of the use of biodiesel on the out DPF particulate emissions and its drawbacks on the management of the regeneration process. In particular, lower particle emissions are observed both during and after the regeneration event. Furthermore, it was observed that the use of RME requires a flexible "management system" that allows the adjustment of the injection strategy according to the fuel properties in order to activate the process and guarantee the complete filter regeneration.

GM Powertrain Europe and Istituto Motori CNR have undergone a research project aimed at studying the effects on engine performance, emissions and fuel consumption of alternative diesel fuels, from both first (FAME) and second (GTL) generation. The present paper reports some of the results achieved studying the impact on injection and spray behavior of rapeseed and soybean methyl-esters, as well as of GTL diesel blends. The test were performed on a Bosch second generation common rail solenoid-driven fuel injection system capable of 1600bar maximum injection pressure, fitted on GM 1.9L Euro4 diesel engine for passenger cars. The characterization of the injection process has been carried out in terms both of fuel injection rate, as well as of spatial and temporal fuel distribution in a quiescent non-evaporative optically accessible chamber. The injection schedules that have been analyzed, as well as the gas density in the spray bomb, have been chosen as representative of different engine working conditions for data correlation, both at partial and full load. Digital processing of the spray images, captured at different instant from the start of injection and for the diverse operating conditions, enabled the spatial and temporal characterization of the fuel in terms of tip penetration and spray-cone angle. Experimental results support the consideration that, at ambient temperature, alternative fuels induce small variations in the injection pattern, in particular the pilot event which is mostly impacted by variations in fuel viscosity and density that affect the needle dynamics. Also spray pattern exhibit very similar behaviour among the different fuels, with deviations over the standard dispersion that are noticeable at low injected quantities. As a consequence, the variations in performance and emissions that were measured on the multi-cylinder engine with the same fuels can be primarily traced back to the chemical composition of the fuel itself and to the drift in engine working point it triggers in torque-based diesel engine controllers.

The combustion propagation and burned-gas expansion processes in a bi-fuel CNG SI engine were characterized by applying a newly developed diagnostic tool, in order to better understand how these processes are related to the fuel composition, to the engine operating variables as well as to the exhaust emissions. The diagnostic tool is based on an original multizone heat-release model that is coupled with a CAD model of the burned-gas containing surface for the computation of the burning speed and the burned-gas mean expansion velocity. Furthermore, the thermal and prompt NO sub-models, embedded in the diagnostic code, were employed to study the effects of NO formation mechanisms and thermodynamic parameters on nitric oxide emissions. A previously developed multivalve bi-fuel SI engine has been upgraded to take a wide experimental database of in-cylinder pressure time-histories, engine performance and pollutant emissions throughout an extended air-fuel ratio interval for both fuels, i.e., gasoline and CNG (up to the lean-combustion stability limit) and an enlarged speed range for CNG (up to 6500 rpm). In particular, the CNG pressure reducer upstream of the injection system was replaced to deliver the gaseous fuel at higher pressures and the CNG injectors were replaced with new injectors purposely designed and realized with larger flow nozzle areas. Experimental tests have thus been carried out in a broad interval of speeds (n = 2000-5500 rpm), loads (bmep = 200-790 kPa), relative air-fuel ratios (RAFR = 0.80-1.60) and spark advances (SA ranging from 8 deg retard to 8 deg advance with respect to MBT timing). One of the main findings was that the ratio between the burning speed Sb and the laminar flame speed SL, at the point of the engine cycle where Sb peaks, scales with n. The scale factors were worked out for both gasoline and CNG operations. The effects of operating engine variables on flame propagation parameters were analyzed

New computational procedures are proposed for evaluating the exhaust brake specific mass emissions of each pollutant species in IC engines. The procedures start from the chemical reaction of fuel with combustion air and, basing on the measured exhaust raw emissions THC, CH4 , NOx , CO, O2 , CO2 , calculate the volume fractions of the compounds in the exhaust gases, including those that are not usually measured, such as water, nitrogen and hydrogen. The method also takes the effects of various fuel and combustion air compositions into account, with particular reference to different natural gas blends as well as to the presence of water vapor, CO2 , Ar and He in the combustion air. The molecular mass of the exhaust gases is then evaluated and the brake specific emissions can be obtained if the exhaust flow rate and the engine power output are measured. The methods stem from the extension of the different procedures that are used in the literature to evaluate α from measured raw volume emissions of IC engines running on conventional fuels. In the present study, a new algorithm is developed so as to generalize and refine all the mentioned α evaluation procedures, keeping conventional and alternative fuel compositions into account. First, the algorithm is applied to the evaluation of α in an automotive bi-fuel SI engine running on gasoline and CNG under a wide range of operating conditions. The α evaluation tests were carried out with a carefully controlled multipoint sequential injection system for both gasoline and CNG fueling. The results are compared to those obtained from the directly measured air and fuel mass flow rates as well as from more conventional UEGO sensor data. The algorithm is then applied to the evaluation of the brake specific mass emission of each pollutant species under gasoline and CNG engine operations for different steady-state working conditions. The sensitivity of results to the main engine working parameters, the influence of environmental conditions (in particular the effect of air humidity on NOx formation) and the experimental uncertainties are determined. The specific emissions calculated from the proposed algorithm are finally compared to those obtained by applying SAE and ISO recommended practices.Copyright © 2003 by ASME

The present paper describes the results of a cooperative research project between GM Powertrain Europe and Istituto Motori - CNR aimed at studying the impact of both fresh and highly oxidized Rapeseed Methyl Ester (RME) at different levels of blending on performance, emissions and fuel consumption of modern automotive diesel engines featuring Closed-Loop Combustion Control (CLCC). In parallel, the capability of this system to detect the level of biodiesel blending through the use of specific detection algorithms was assessed. The tests were performed on the recently released 2.0L Euro5 GM diesel engine for passenger car application equipped with embedded pressure sensors in the glow plugs. Various blends of fresh and aged RME with reference diesel fuel were tested, notably 20% RME by volume (B20), 50% (B50) and pure RME (B100). The tests on the multi-cylinder engine were carried out in a wide range of engine operating points for the complete characterization of the biodiesel performance in the New European Driving Cycle (NEDC). The results highlighted that there is not appreciable difference in terms of performance and emission between fresh and oxidized biodiesel, at all levels of blending. On the other hand, the capability of the CLCC control to detect biodiesel blending with reasonable accuracy and to implement the corrective actions for avoiding emission drift and performance losses was successfully demonstrated.