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Latest emissions standards impose very low NOx and particle emissions that have led to new Diesel combustion operating conditions, such as low temperature combustion (LTC). The principle of LTC is based on enhancing air fuel mixing and reducing combustion temperature, reducing raw nitrogen oxides (NOx) and particle emissions. However, new difficulties have arisen. LTC is typically achieved through high dilution rates and low CR, resulting in increased auto-ignition delay that produces significant noise and deteriorates the combustion phasing. At the same time, lower combustion temperature and reduced oxygen concentration increases hydrocarbon (HC) and carbon oxide (CO) emissions, which can be problematic at low load. Therefore, if LTC is a promising solution to meet future emission regulations, it imposes a new emissions, fuel consumption and noise trade-off. For this, the injection strategy is the most direct mean of controlling the heat release profile and fuel air mixture.

Among the existing concepts that help to improve the efficiency of spark-ignition engines at part load, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions. This combustion concept is based on the auto-ignition of an air-fuel-mixture highly diluted with hot burnt gases to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. To minimize the costs of conversion of a standard spark-ignition engine into a CAI engine, the present study is restricted to a Port Fuel Injection engine with a cam-profile switching system and a cam phaser on both intake and exhaust sides. In a 4-stroke engine, a large amount of burnt gases can be trapped in the cylinder via early closure of the exhaust valves. This so-called Negative Valve Overlap (NVO) strategy has a key parameter to control the amount of trapped burnt gases and consequently the combustion: the exhaust valve-lift profile.

While fuel efficiency has to be improved, future Diesel engine emission standards will further restrict vehicle emissions, particularly of nitrogen oxides. Increased in-cylinder filling is recognized as a key factor in addressing this issue, which calls for advanced design of air and exhaust gas recirculation circuits and high cooling capabilities. As one possible solution, this paper presents a 2-stage boosting breathing architecture, specially dedicated to improving the trade-off between emissions and fuel consumption instead of seeking to improve specific power on a large family vehicle equipped with a 1.6-liter Diesel engine. In order to do it, turbocharger matching was specifically optimized to minimize engine-out NOx emissions at part-load and consumption under common driving conditions. Engine speed and load were analyzed on the European driving cycle. The key operating points and associated upper boundary for NOx emission were identified.

The simultaneous reduction of engine-out nitrogen oxide (NOx) and particulate emissions via low-temperature combustion (LTC) strategies for compression-ignition engines is generally achieved via the use of high levels of exhaust gas recirculation (EGR). High EGR rates not only result in a drastic reduction of combustion temperatures to mitigate thermal NOx formation but also increases the level of pre-mixing thereby limiting particulate (soot) formation. However, highly pre-mixed combustion strategies such as LTC are usually limited at higher loads by excessively high heat release rates leading to unacceptable levels of combustion noise and particulate emissions. Further increasing the level of charge dilution (via EGR) can help to reduce combustion noise but maximum EGR rates are ultimately restricted by turbocharger and EGR path technologies.

Single cylinder optical engines are used for internal combustion (IC) engine research as they allow for the application of qualitative and quantitative non-intrusive, diagnostic techniques to study in-cylinder flow, mixing, combustion and emissions phenomena. Such experimental data is not only important for the validation of computational models but can also provide a detailed insight into the physical processes occurring in-cylinder which is useful for the further development of new combustion strategies such as gasoline homogeneous charge compression ignition (HCCI) and Diesel low temperature combustion (LTC). In this context, it is therefore important to ensure that the performance of optical engines is comparable to standard all-metal engines. A comparison of optical and all-metal engine combustion and emissions performance was performed within the present study.

The authors present the supervisory control of a parallel hybrid powertrain, focusing on several issues related to the real-time implementation of optimal control based techniques, such as the Equivalent Consumption Minimization Strategies (ECMS). Real-time implementation is introduced as an intermediate step of a complete chain of tools aimed at investigating the supervisory control problem. These tools comprise an offline optimizer based on Pontryagin Minimum Principle (PMP), a two-layer real-time control structure, and a modular engine-in-the-loop test bench. Control results are presented for a regulatory drive cycle with the aim of illustrating the benefits of optimal control in terms of fuel economy, the role of the optimization constraints dictated by drivability requirements, and the effectiveness of the feedback rule proposed for the adaptation of the equivalence factor (Lagrange multiplier).

The combination of air charging and downsizing is known to be an efficient solution to reduce CO2 emissions of modern gasoline engines. The decrease of the cubic capacity and the increase of the specific performance help to reduce the fuel consumption by limiting pumping and friction losses and even the losses of energy by heat transfer. Investigations have been conducted on a highly downsized SI engine to confirm if a strong decrease of the displacement (50 %) was still interesting regarding the fuel consumption reduction and if other ways were possible to improve further more its efficiency. The first aim of our work was to identify the optimal design (bore, stroke, displacement, …) that could maximize the consumption reduction potential at part load but also improve the engine's behaviour at very high load (up to 3.0 MPa IMEP from 1000 rpm). In order to do that, four engine configurations with different strokes and bores have been tested and compared.

Facing the CO2 emission reduction challenge, the combination of downsizing and turbocharging appears as one of the most promising solution for the development of high efficiency gasoline engines. In this context, as knock resistance is a major issue, limiting the performances of turbocharged downsized gasoline engines, fuel properties are more than ever key parameters to achieve high performances and low fuel consumption's levels. This paper presents a combustion study carried out into the GSM consortium of fuel quality effects on the performances of a downsized turbocharged Direct Injection SI engine. The formulation of two adapted fuel matrix has allowed to separate and evaluate the impacts of three major fuel properties: Research Octane Number (RON), Motor Octane Number (MON) and Latent Heat of Vaporization (LHV). Engine tests were performed on a single cylinder engine at steady state operating condition.

More and more stringent restrictions concerning the pollutant emissions of ICE (Internal Combustion Engines) constitute a major challenge for the automotive industry. New combustion strategies such as LTC (Low Temperature Combustion), PCCI (Premixed Controlled Compression Ignition) or HCCI (Homogeneous Charge Compression Ignition) are promising solutions to achieve the imposed emission standards. They permit low NOx and soot emissions via a lean and highly diluted combustion regime, thus assuring low combustion temperatures. In next generation of ICE, new technologies allow the implementation of complex injection strategies in order to optimize the combustion process. This requires the creation of numerical tools adapted to these new challenges. This paper presents a 0D Diesel HCCI combustion model based on a physical 3D CFD (Computational Fluid Dynamics) approach.

This paper presents the detailed characterization of particulate emissions from a NADI™ dual mode engine (HCCI at low load and conventional combustion at high load). Morphology, composition and chemical reactivity of the particulate matter generated on an engine running in HCCI mode have been specified and compared to the conventional mode reference. Results showed that HCCI combustion formed particles with a higher volatile organic fraction due to the relatively high level of HC generated by this kind of combustion. Advanced soot characterization emphasized that HCCI soot is oxidized at a slower reaction rate than conventional soot, but with a lower temperature. This last characteristic could partially compensate the poor continuous regeneration effect due to low NO2 emission levels observed in HCCI combustion. Microscopic observation and particle sizing did not show significant differences between HCCI and conventional soot.

Engine downsizing is one of the most promising engine solutions to improve efficiency, but requires higher specific performance because of a lower engine displacement. The study is based on experimental work performed with an IFP prototype single cylinder engine, representative of passenger car applications. This engine enables very high specific power, with a high level of thermal and mechanical constraints. Tests were carried out on both full load and part load operation with a prototype common rail equipment capable of very high fuel pressure (up to 250 MPa). Results show that increasing fuel flow rate using fuel injection pressure instead of increasing nozzle hole diameter is more advantageous at full load, mainly because a lower nozzle hole diameter improves air entrainment. Benefits observed with increased injection pressure are enhanced when associated with upgraded engine thermo-mechanical limits, and advanced turbo charging system.

This work studies the potential of ethanol-Biodiesel-Diesel fuel blends in both conventional Diesel and HCCI combustion modes. First, ethanol based fuels were tested on a modern commercial multi-cylinder DI diesel engine. The aim of this phase was to assess how such fuels affect Diesel engine performances and emissions. These results indicate that low levels of PM and NOx emissions, with a contained fuel consumption penalty and with an acceptable noise level, are achievable when the Diesel-ethanol blends are used in combination with an optimized combustion control. Moreover, experiments with ethanol based blends were performed using a single cylinder engine, running under both early injection HCCI and Diesel combustion modes. Compared to a conventional fuel, these blends allow increasing the HCCI operating range and also lead to higher maximum power output in conventional Diesel combustion.

New combustion processes like LTC (Low Temperature Combustion) that includes HCCI (Homogeneous Charge Compression Ignition), PCCI (Premixed Charge Compression Ignition), PPCI (Partial Premixed Compression Ignition)… are promising ways to reduce simultaneously NOx and PM. Nevertheless, these combustion processes can be used only on a limited part of the engine load and speed map. Therefore, it appeared interesting to assess how the fuel, through its characteristics, could enhance the operating range in such combustion processes. That was the aim of an international consortium carried out by IFP and supported by numerous industrial companies. First a specific procedure has been developed to compare the different fuels on a early injection HCCI single cylinder engine. Then, using this procedure, a matrix of fuels having different cetane numbers (CN = 40-63), volatilities and chemical compositions has been tested.

The reduction of NOx emissions required by the future Euro 6 standards leads engine manufacturers to develop Diesel Homogeneous Charge Compression Ignition (HCCI) combustion processes. Because this concept allows reducing both NOx and particulates simultaneously, it appears as a promising way to meet the next environmental challenges. Unfortunately, HCCI combustion often increases CO and HC emissions. Conventional oxidation catalyst technologies, currently used for Euro 4 vehicles, may not be able to convert these emissions because of the saturation of active catalytic sites. As a result, such increased CO and HC emissions have to be reduced under standard levels using innovative catalysts or emergent technologies. The work reported in this paper has been conducted within the framework of the PAGODE project (PSA, IFP, Chalmers University, APTL, CRF, Johnson Matthey and Supelec) and financed by the European Commission.

Environment protection issues regarding CO2 emissions as well as customers requirements for fun-to-drive and fuel economy explain the strong increase of Diesel engine on European market share in all passenger car segments. To comply future purposes of emission regulations, particularly dramatic decrease in NOx emissions, technology need to keep upgrading; the reduction of the volumetric compression ratio (VCR) is one of the most promising research ways to allow a simultaneous increase in power at full load and NOx / PM trade-off improvement at part load. This study describes the combustion effects of the reduction of compression ratio and quantifies improvements obtained at full load and part load running conditions on a HSDI Common Rail engine out performance (power, fuel consumption, emissions and noise). Potential and limitations of a reduced compression ratio from 18:1 to 14:1 are underlined.

Low temperature combustion concept as HCCI is one of the most promising research ways to comply future emission regulations of Diesel passenger vehicles. IFP promoted this concept with NADI™ (Narrow Angle Direct Injection) combustion design whose original approach lies on a fuel spray guided by the bowl central tip to the re-entrant. For full load operating range, one of the key issue for success is to use as much as possible available air in the combustion chamber in order to reach low value of air fuel ratio, and therefore high value of specific power and specific torque. In this study, engine tests on a single cylinder engine with NADI™ concept are performed at full load; 3-D calculations as well as air/fuel mixing process visualizations in a constant volume vessel with optical access allowed to establish criteria for helping future combustion system design for full load operation.

In former high compression ratio Diesel engines a single injection was used to introduce the fuel into the combustion chamber. With actual direct injection engines which exhibit a compression ratio between 17:1 and 18:1 single or multiple early injections called “pilot injections” are also added in order to reduce the combustion noise. For after-treatment reasons a late injection during the expansion stroke named “post injection” may also be used in some operating conditions. Investigations have been conducted on lower compression ratio Diesel engine and in high EGR rate operating conditions to evaluate the benefits of multiple injection strategies to improve the trade off between engine emissions, noise and fuel economy.

The recent development of biofuel production worldwide is closely linked to GHG savings objectives and to regional agricultural policies. Many existing studies intend to evaluate the net non renewable energy and GHG savings associated to the various biofuel production pathways. However, there is no consensus on the results of those studies. The main explanations of variations among the results are the following: energy consumption and GHG emissions of the reference fossil pathway, data used for the representation of farming processes and biofuel production processes, accounting for carbon storage in agricultural soils, reference use of the land, choice of an allocation method in case of coproduction. There is a strong drive in the European Union for a certification on the sustainability of biofuel pathways.

The formation mechanisms of unburned hydrocarbons (HC) in low NOx, homogeneous type Diesel combustion have been investigated in both standard and optical access single cylinder engines operating under low load (2 and 4 bar IMEP) conditions. In the standard (i.e. non-optical) engine, parameters such as injection timing, intake temperature and global equivalence ratio were varied in order to analyse the role of bulk quenching on HC emissions formation. Laser-induced fluorescence (LIF) imaging of in-cylinder unburned HC within the bulk gases was performed on the optical-access engine. Furthermore, studies were performed in order to ascertain whether the piston top-land crevice volume contributes significantly to engine-out HC emissions. Finally, the role of piston-top fuel films and their impact on HC emissions was studied. This was investigated on the all-metal engine using two fuels of different volatilities.

In the context of increasingly stringent pollution norms, reduced engine emissions are a great challenge for compressed ignition engines. After-treatment solutions are expensive and very complex to implement, while the NOx/PM trade-off is difficult to optimise for conventional Diesel engines. Therefore, in-cylinder pollutant production limitation by the HPC combustion mode (Highly Premixed Combustion) - including Homogeneous Charge Compression Ignition (HCCI) - represents one of the most promising ways for new generation of CI engine. For this combustion technology, control based on torque estimation is crucial: the objectives are to accurately control the cylinder-individual fuel injected mass and to adapt the fuel injection parameters to the in-cylinder conditions (fresh air and burned gas masses and temperature).