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Pollutants emissions from transportation have become a major focus of environmental concerns in the last decades. Many alternative fuels are under consideration, among which Natural Gas as fossil resource offering an advantageous potential to reduce local emissions. The European Commission has set an objective of 10% of Natural Gas consumption for the transport sector by 2020. In a sustainable development view, both vehicle emissions and energy supply chain analysis from well to wheel must be addressed. Even if the main focus today is on CO2 emissions, it is interesting to evaluate the pollutant emissions of the whole Well to Wheel chain. Besides, as the potential of reducing pollutant emissions of vehicle (due to the improvement of engines and severization of norms), looking at pollutant emissions of the Well to Tank part of the chain could show the possible further improvements. Former studies exist, comparing Natural Gas to conventional and non conventional fuels.

Quantitative fuel concentration visualizations are carried out to study the mixing process between fuel and air in Direct Injection (DI) Diesel like conditions, and generate high quality data for the validation of mixing models. In order to avoid the particular complication connected with fuel droplets, a gaseous fuel jet is investigated. Measurements are performed in a high-pressure chamber that can provide conditions similar to those in a diesel engine. A gas injection system able to perform injections in a high-pressure chamber with a good control of the boundary conditions is chosen and characterized. Mass flow rates typical of DI Diesel injection are reproduced. A Laser Induced Fluorescence technique requiring the mixing at high pressure of the fluorescent tracer, biacetyl, with the gaseous fuel, methane, is developed. This experimental technique is able to provide quantitative measurement of fuel concentration in high-pressure jets.

Compressed natural gas (CNG) is considered as one of the most promising alternative fuels for transportation due to its ability to reduce greenhouse gas emissions (CO2, in particular) and its abundance. An earlier study from IFP has shown that CNG has a considerable potential when used as a fuel for a dedicated downsized turbo-charged SI engine on a small urban vehicle. To take further advantage of CNG assets, this approach can be profitably extended by adding a small secondary (electrical) power source to the CNG engine, thus hybridizing the powertrain. This is precisely the focus of the new IFP project, VEHGAN, which aims to develop a mild-hybrid CNG prototype vehicle based on a MCC smart car equipped with a reversible starter-alternator and ultra-capacitors (Valeo Starter Alternator Reversible System, StARS).

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.

Among the last years, environmental concerns have raised the interest for biofuels. Ethanol, blended with gasoline seems particularly suited for the operation of internal combustion engines, and has been in use for severals years in some countries. However, it has a strong impact on engine performance, which is emphasized on recent engine architectures, with downsizing through turbocharging and variable valve actuation. Taking all the benefits of ethanol-blended fuel thus requires an adaptation of the engine management system. This paper intends to assess the effect of gasoline-ethanol blending from this point of view, then to describe a mean-value model of a fuel-flexible turbocharged PFI-SI engine, which will serve as a basis for the development of control algorithms. The focus will be in this paper on ethanol content estimation in the blend, supported by both simulation and experimental results.

Currently, the development of higher specific output and higher efficiency S.I. engines requires better control and knowledge of knock mechanisms. As it is not easily possible to instrument an engine to determine the beginning of fuel auto-ignition, knock modeling by means of 3D CFD simulation, can be a powerful tool to understand and try to avoid this phenomenon [1, 2, 3]. The objectives of the work described in this paper are to develop and validate a simple model of auto-ignition. This model, developed at IFP, is implemented in the 3D CFD code KMB [4, 5]. It is based on an AnB model [6, 7] which creates a ‘precursor’ species transported with the flow in the combustion chamber. When its concentration reaches a limiting value, the auto-ignition phenomenon occurs.

Recent developments on highly downsized spark ignition engines have been focused on knocking behaviour improvement and the most advanced technologies combination can face up to 2.5 MPa IMEP while maintaining acceptable fuel consumption. Unfortunately, knocking is not the only limit that strongly downsized engines have to confront. The improvement of low-end torque is limited by another abnormal combustion which appears as a random pre-ignition. This violent phenomenon which emits a sharp metallic noise is unacceptable even on modern supercharged gasoline engines because of the great pressure rise that it causes in the cylinder (up to 20 MPa). The phases of this abnormal combustion have been analysed and a global mechanism has been identified consisting of a local ignition before the spark, followed by a propagating phase and ended by a massive auto-ignition. This last step finally causes a steep pressure rise and pressure oscillations.

The benefits of running on ethanol-blended fuels are well known, especially global CO₂ reduction and performances increase. But using ethanol as a fuel is not drawbacks free. Cold start ability and vehicle autonomy are appreciably reduced. These two drawbacks have been tackled recently by IFP and its partners VALEO and Cristal Union. This article will focus on the second one, as IFP had the responsibility to design the powertrain of a fully flex-fuel vehicle (from 0 to 100% of ethanol) with two main targets: reduce the fuel consumption of the vehicle and maintain (at least) the vehicle performances. Using a MPI scavenging in-house concept together with turbocharging, as well as choosing the appropriate compression ratio, IFP managed to reach the goals.

In order to determine the area where knock occurs in a single cylinder engine, an acoustic methodology needs a minimum of four simultaneous pressure measurements in the combustion chamber. A specific cylinder head gasket integrating 12 pressure sensors has been developed and tested. The gasket is based on a bonded multilayer technology including high temperature piezoelectric cells, metallic and insulating sheets and printed circuit films. The total thickness is close to 1.25 mm (1/20 inch) and allows a straight forward substitution of the original gasket without modification. The sensors have large frequency bandwidth (typically 3-100 kHz) and withstand severe conditions (heat, combustion, pressure, vibrations, static pre-stress, electromagnetic fields and shocks). Signal processing adaptation of the dedicated exploitation software has brought good success for the single cylinder prototype, which remains operational after 100 hours of extreme conditions running (high knock).

Due to their high thermal efficiency coupled with low CO2 emissions, Diesel engines are promised to an increasing part of the transport market if their NOx and particulate emissions are reduced. Today, adequate after-treatments, NOx and PM traps are under industrialization with still concerns about fuel economy, robustness, sensitivity to fuel sulfur and cost because of their complex and sophisticated strategy. New combustion process such as Homogeneous Charge Compression Ignition (HCCI) are investigated for their potential to achieve near zero particulate and NOx emissions. Their main drawbacks are too high hydrocarbons (HC) and carbon monoxide (CO) emissions, combustion control at high load and then limited operating range and power output. As an answer for challenges the Diesel engine is facing, IFP has developed a combustion system able to reach near zero particulate and NOx emissions while maintaining performance standards of the D.I Diesel engines.

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 introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap. This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR.

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.

Facing more and more stringent regulations, new solutions are developed to decrease pollutant emissions. One of them have shown promising and relevant results. It consists of the use of ethanol as a blending component for diesel fuel Nevertheless, the addition of ethanol to Diesel fuel affects some key properties such as the flash point. Consequently, Diesel blends containing ethanol become highly flammable at a temperature around ambient temperature. This study proposes to improve the formulation of ethanol based diesel fuel in order to avoid flash point drawbacks. First, a focus on physical and chemical properties is done for ethanol based diesel fuels with and without flash point improvement. Second, blends are tested on a passenger car diesel engine, under a wide operating range conditions from low load low speed up to maximum power. The main advantage of the ethanol based fuels generate low smoke level, that allows using higher EGR rate, thus leading to an important NOx decrease.

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.

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.

Modelling small and large scale fluctuations of fuel distribution is of high interest for stratified direct injection spark ignition (DISI) engines. Homogeneous combustion models need to be extended or replaced in order to account for these fluctuations. They are presently neglected in most engine simulations. Effects of mean fuel/air equivalence ratio gradient have been recently included in previous homogeneous mixture approaches. To account for local fluctuations of mixture composition, the new model ECFM-Z has been developed on the basis of recent Direct Numerical Simulation results and Coherent Flame Surface modelling. The model has been implemented in a CFD code (KMB) The influence of mixture fraction is integrated in the Extended Coherent Flame Surface combustion model. The model is based on a conditional approach. Unburnt hydrocarbons produced by lean flame local extinctions are taken into account.

Among the existing concepts to help improve the efficiency of spark ignition engines on low load operating points, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions at part load without major modifications of the engine design. The CAI™ concept is founded on the auto-ignition of a highly diluted gasoline-based mixture in order to reach high indicated efficiency and low pollutant emissions through a low temperature combustion. Previous research works have demonstrated that the valve strategy is an efficient way to control the CAI™ combustion mode. Not only the valve strategy has an impact on the amount of trapped burnt gases and their temperature, but also different valve strategies can lead to equivalent mean in-cylinder conditions but clearly differentiated combustion timing or location. This is thought to be the consequence of local mixture variations acting in turn on the chemical kinetics.

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 without major modifications of the engine design. The CAI™ concept is based on the auto-ignition of a fuel mixture highly diluted with burnt gases in order to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. In a 4-stroke engine, large amounts of burnt gases can be trapped in the cylinder by re-breathing them through the exhaust ports during the intake stroke using a 2-step exhaust valve-lift profile. The interaction between the intake and exhaust flows during the intake stroke was identified as a key parameter to control the subsequent combustion in a CAI™ PFI engine. Consequently, the intake valve-lift profile as well as the exhaust re-opening profile can potentially be used as control parameters for this combustion mode.

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 without major modifications of the engine design. The CAI™ concept is based on the auto-ignition of a fuel mixture highly diluted with burnt gases in order to achieve high indicated efficiency and low pollutant emissions through low temperature combustion. Large amounts of burnt gases can be trapped in the cylinder by re-breathing them through the exhaust ports during the intake stroke. For that, a 2-step exhaust valve-lift profile is used. The interaction between the intake and exhaust flows during the intake stroke was identified as a key parameter to control the subsequent combustion in a CAI™ port fuel injected (PFI) engine.