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A single cylinder Diesel engine was used to study combustion stability changes from a cetane number improver: 2-EHN. It has been added to a low cetane number diesel and two biodiesels blends with 20 % of SME or RME. All fuels have been raised to a CN of 51 with 2-EHN. Those fuels have been compared to a reference diesel with a CN of 55. Cold and warm start have been recreated for measurements at three conditions: cranking, engine speed increase and idle. Engine coolant temperature has been set to 20°C and 80°C for cold and warm start respectively. 2-EHN effects on combustion stability have been monitored through the IMEP covariance. Under cold-start, only the low cetane number diesel showed combustion stabilities improvements with 2-EHN addition. Moreover, the combustion stability was better than the reference diesel and the heat release rate show an enhancement of the cold flame. On the contrary, the biodiesel fuels exhibited higher IMEP covariances.

A single cylinder Diesel engine was used to study LTC combustion. We evaluated the 2-EthylHexyl Nitrate (2-EHN) as cetane number improver (CNI) distributed by VeryOne@ on the combustion of six diesel fuels. Tested fuels are a low Cetane Number (CN) diesel fuel (CN of 43.7) and two biodiesel mixed at 20% with the low Cetane number diesel fuel: Soybean oil Methyl Ester (B100 SME) and Rapeseed oil Methyl Ester (B100 RME). Each fuels doped with the 2-EHN were prepared to meet the minimum European CN, 51. LTC strategies could provide low NOx emission without thermal efficiency deterioration. The study investigated engine operation at loads of 2, 6 and 10 bar IMEP at engine speed of 1250 rpm, 1500 rpm and 2000 rpm and the impact against synthetic EGR up to 30%. The low-temperature decomposition of 2-EHN, resulting in the oxidation of the fuel, makes it possible to achieve a very low cycle-to-cycle variation of the IMEP even at very low load or at a very high rate of EGR.

Mechanisms responsible for enhanced charge reactivity with intake added ozone (O3) were explored in a single-cylinder, optically accessible, research engine configured for low-load advanced compression ignition (ACI) experiments. The influence of O3 concentration (0-40 ppm) on engine performance metrics was evaluated as a function of intake temperature and start of injection for the engine fueled by iso-octane, 1-hexene, or a 5-component gasoline surrogate. For the engine fueled by either the gasoline surrogate or 1-hexene, 25 ppm of added O3 reduced the intake temperature required for stable combustion by 65 and 80°C, respectively. An ultraviolet (UV) light absorption diagnostic was also used to measure crank angle (CA) resolved in-cylinder O3 concentrations for select motored and fired operating conditions. The O3 measurements were compared to results from complementary 0D chemical kinetic simulations that utilized detailed chemistry mechanisms augmented with O3 oxidation chemistry.

In an optical Homogeneous Charge Compression Ignition (HCCI) engine, experiments were performed to study the combustion of different surrogate fuels (n-heptane, 75%n-heptane/25%isooctane, 80%n-heptane/20%toluene). The effect of laboratory simulated EGR rates, inlet temperatures and the presence of different chemical species in the EGR on the ignition combustion timings were analyzed at a fixed equivalence ratio (0.3). The mixture homogeneity was verified by Laser-Induced-Fluorescence on the toluene. The experimental results affirm that the EGR delays the combustion unlike the inlet temperature. Intake CO and CH4 addition has no effect on ignition timings whereas a promoting effect of NO is checked. A zero-dimensional model was developed and offered encouraging tendencies by comparison with the experiments.

A low swirl, low compression ratio engine with narrow fuel spray angle injector was used to investigate the cylinder wall wetting process of early direct injection strategies. A methodology was developed in order to detect liquid fuel impingement on the cylinder wall oil film. First, single injection tests were performed in order to investigate the effect of injection pressure and start of injection on the amount of fuel that can be injected in the combustion chamber without liquid fuel cylinder wall impingement. Then double injection strategies were performed to verify the existence of interactions between successive injections for early injection thermodynamic conditions. Finally an optimization of the injection strategy maximizing the fuel quantity without cylinder wall wetting is proposed. Results obtained for single early direct injection show that all conditions of injection timing during the intake stroke lead to cylinder wall wetting above a given injected mass.

We present an experimental investigation of the local flame front characteristics as function of the distance between the flame front and the piston. The objective of this paper is to provide some experimental data about the flame characteristics at the approach of the piston. The transparent engine speed is fixed at 2000 rpm and air-methane mixture was used with an equivalence ratio equal to 0.9. PLIF acetone imaging was acquired to estimate first the curvature, the curvature radius and the normal direction orientation of the local contours as function of the flame-piston distance. A discontinuity in these parameters appears when the distance is less than 1 mm. Secondly we apply local roughness analysis system to estimate the local fractal dimension of the flame front. We conclude that fractal dimension changes rapidly at 2.5 mm from the piston. A logarithm law was found to define the fractal dimension as function of flame-piston distance.

Gasoline Compression Ignition (GCI) engines based on Gasoline Partially Premixed Combustion (GPPC) showed potential for high efficiency and reduced emissions of NOx and Soot. However, because of the high octane number of gasoline, misfire and unstable combustion dramatically limit low load operating conditions. In previous work, seeding the intake of the engine with ozone showed potential for increasing the fuel reactivity of gasoline. The objective of this work was to evaluate the potential of ozone to overcome the low load limitations of a GCI engine. Experiments were performed in a single-cylinder light-duty CI engine fueled with 95 RON gasoline. Engine speed was set to 1500 rpm and intake pressure was set to 1 bar in order to investigate typical low load operating conditions. In the first part of the work, the effect of ozone on gasoline autoignition was investigate while the start of the fuel injection varied between 60 CAD and 24 CAD before TDC.

Ammonia and hydrogen can be produced from water, air and excess renewable electricity (Power-to-fuel) and are therefore a promising alternative in the transition from fossil fuel energy to cleaner energy sources. An Homogeneous-Charge Compression-Ignition (HCCI) engine is therefore being studied to use both fuels under a variable blending ratio for Combined Heat and Power (CHP) production. Due to the high auto-ignition resistance of ammonia, hydrogen is required to promote and stabilize the HCCI combustion. Therefore the research objective is to investigate the HCCI combustion of varying hydrogen-ammonia blending ratios in a 16:1 compression ratio engine. A specific focus is put on maximizing the ammonia proportion as well as minimizing the NOx emissions that could arise from the nitrogen contained in the ammonia. A single-cylinder, constant speed, HCCI engine has been used with an intake pressure varied from 1 to 1.5 bar and with intake temperatures ranging from 428 to 473 K.

The transportation sector adds to the greenhouse gas emissions worldwide. One way to decrease this impact from transportation is by using renewable fuels. Ethanol is a readily available blend component which can be produced from bio blend­stock, currently used blended with gasoline from low to high concentrations. This study focuses on a high octane (RON=97) gasoline blended with 0, 20, and 50, volume % of ethanol, respectively. The high ethanol blended gasoline was used in a light duty engine originally designed for diesel combustion. Due to the high octane rating and high ignition resistance of the fuel it required high intake temperatures of 443 K and higher to achieve stable combustion in in homogeneously charged compression ignition (HCCI) combustion operation at low load. To enable combustion with lower intake temperatures more commonly used in commercial vehicles, ozone was injected with the intake air as an ignition improver.

Increasingly stringent pollutant emission regulations have constrained car manufacturers to reduce the fuel consumption and pollutant emissions of internal combustion engines. Downsized engines appear to be the most promising way to achieve this in terms of emission reduction as well as investment minimization. The design of downsized internal combustion engines requires the understanding and quantification of thermo-fluid-dynamic processes at high pressure, high temperature and with high dilution rate. This study aims to carry out preparatory work in a fan-stirred spherical combustion vessel at conditions representative of those occurring in downsized engines. First, experimental correlations giving the laminar burning velocity from the initial pressure, the initial temperature, the dilution rate and the equivalence ratio are proposed.

Nowadays, the main objectives in the automobile engine field are to reduce fuel consumption and pollutant emissions. HCCI engines can be a good solution to meet pollutant emission requirements and to achieve high combustion efficiency. However, before an HCCI engine is used as a conventional engine, several problems must be overcome, in particular control of the progression of combustion. Many studies have been conducted into possible control methods. A new strategy consists in using oxidizing chemical species such as ozone to seed the intake of a HCCI engine. As increasingly smaller ozonizers are now being designed, this kind of device could be integrated on a vehicle and on a HCCI engine, in order to control combustion phasing and promote the future use of this engine as a conventional engine. In the present study, experiments on a HCCI engine fuelled with iso-octane were carried out with ozone seeding in the intake.

Fossil fuel reserves are being depleted due to increasing energy requirements. One of the solutions is to partly replace fossil fuel by renewable biodiesel fuel. However, the physical properties of biodiesel fuels need to be thoroughly investigated before applying biodiesel or diesel-biodiesel blends in diesel engines, in order to improve the combustion efficiency. This paper presents the experimental study of diesel fuel and biodiesel blends on injection flow characteristics and fuel spray behavior. Seven fuels were tested: diesel fuel, five diesel-biodiesel blends: 10%(B10), 20%(B20), 30%(B30), 40%(B40), 50%(B50), and pure biodiesel(B100) in a diesel engine equipped with a piezo injector. Injection pressures were set at 30-180 MPa for the study of the injection flow characteristics and at 30-150 MPa for the study of spray behavior in non-vaporizing conditions.

As an alternative to second generation ethanol, valeric esters can be produced from lignocellulose through levulinic acid. While some data on these fuels are available, only few experiments have been performed to analyze their combustion characteristics under engine conditions. Using a traditional spark ignition engine converted to mono-cylinder operation, we have investigated the engine performances and emissions of methyl and ethyl valerates. This paper compares the experimental results for pure valeric esters and for blends of 20% of esters in PRF95, with PRF95 as the reference fuel. The esters propagate faster than PRF95 which requires a slight change of ignition timing to optimise the work output. However, both the performances and the emissions are not significantly changed compared to the reference. Accordingly, methyl and ethyl valerate represent very good alternatives as biofuels for SI engines.

Plasma sustained ignition systems are promising alternatives to conventional spark plugs for those applications where the conditions inside the combustion chamber are more severe for spark plug operation, like internal combustion engines with high compression ratio values and with intake charge dilution. This paper shows the results of an experimental activity performed on a spark ignition engine equipped alternatively with a conventional spark plug and a radio frequency sustained plasma ignition system (RFSI). Results showed that RFSI improved engine efficiency, extended the lean limit of combustion and reduced cycle-by-cycle variability, compared with the conventional spark plug at all test conditions. The adoption of the RFSI also had a positive impact on carbon monoxide and unburned hydrocarbon emissions, whereas nitrogen oxide emissions increased due to higher temperatures attained in the combustion chamber.

In the present study, experiments were carried out in a single-cylinder downsized SI engine with different rates of oxygen (15% to 27% by volume in the total mixture of intake gases except fuel) and equivalence ratios (from 0.45 to 1). Therefore, the oxygen volume fraction is due to oxygen enrichment or nitrogen dilution. The study of the impact of controlling oxygen concentration on the combustion characteristics and emissions was performed at 1400 rpm, at several loads (Indicated Mean Effective Pressure (IMEP) from 400 to 1000 kPa). For each operation point, the spark advance and the intake pressure were adjusted simultaneously in order to maintain the load and obtain a minimum value of indicated Specific Fuel Consumption (SFC). The effect of oxygen concentration on the engine combustion characteristics was simulated by using the commercial software AMESim, with the combustion model developed by IFP-EN, and an adapted algorithm was used to avoid residual gas calibration.

Recent works have demonstrated the possibility of operating compression ignition engine with high resistance to auto-ignition fuels as gasoline. By using gasoline and dilution by exhaust gas recirculation, compression ignition can reach high efficiencies and low particulate (PM) and NOx emissions. One of the promising strategies to reach this combustion is the Gasoline Partially Premixed Combustion (GPPC) concept. First step of the study was to optimize the run of a single cylinder Diesel engine in GPPC with double injections strategy by change the second injection phasing and EGR level. The optimum in terms of heat release rate and regulated pollutant emissions was obtained for second injection timing around TDC and an EGR level at 30%.

Homogeneous Charge Compression Ignition (HCCI) is among the new generation of combustion modes which can be applied to internal combustion engines. It is currently the topic of numerous studies in various fields. Due to its operating process, HCCI ensures a good efficiency, similar to that of compression ignition (CI) engines, and low particulate and nitric oxide (NOx) emissions. However, before promoting the use of this kind of engine, several challenges must be addressed, in particular controlling the combustion. Recent work showed that the combustion phasing can be controlled using low concentrations of ozone, an oxidizing chemical species. As ozone generators become increasingly compact, the integration of this kind of device in passenger cars can be considered. The present study investigates the effect of ozone on the combustion of different fuel mixtures. The engine was fuelled with various blends: a 95%methane/5%propane mixture and three different methane/hydrogen mixtures.

Internal combustion engine downsizing allows the reduction of fuel consumption, in particular for those applications where the engine operates frequently at part load conditions. This design solution is usually combined with intake charge dilution by means of exhaust gas recirculation, for the purpose of limiting abnormal combustion events, reducing pumping losses and nitrogen oxide formation. While the exhaust gas recirculation is widely used in compression ignition engines, it still causes some technological issues, in particular for spark ignition engines. This paper presents the results of an experimental campaign performed on a spark ignition engine for the investigation of different dilution techniques for low temperature combustion. Nitrogen, carbon dioxide and exhaust gas recirculation have been adopted as diluents, comparing engine performance and pollutant emissions.

In this work, the first injection of gasoline was maintained at 30 CAD Before TDC and the second one was swept between 10 CAD Before TDC to 5 CAD After TDC, in order to demonstrate the ideal positioning of the second injection. The results showed that when it was placed near TDC, low emissions, acceptable noise and acceptable efficiencies could be obtained. The effect of EGR, simulated by N2 addition, was also studied. As expected, globally the effect of the EGR rate was to delay the combustion phasing and to decrease NOx emissions. The optimal EGR dilution rate was found to be 30% with respect to the cycle-to-cycle variation criterion (< 5%). Increasing the dilution rate increased HC, CO and PM emissions, due to a considerable delay in combustion phasing caused by the reduction in the fuel reaction rate and the in-cylinder lack of oxygen when the EGR rate reached 30%. The impact of the fuel mass distribution between the two injections was also considered.

Increasing the internal combustion engine efficiency is necessary to decrease their environmental impact. Several combustion systems demonstrated the interest of low temperature combustion to move toward this objective. However, to ensure a stable combustion, the use of additives has been considered in a several studies. Amongst them, 2-Ethylhexyl nitrate (EHN) is considered as a good candidate for these systems but characterizing its chemical effect is required to optimize its use. In this study, its promoting effect (0.1 - 1% mol.) on combustion has been investigated experimentally and numerically in order to better characterize its behavior under different thermodynamic and mixture. Rapid compression machine (RCM) experiments were carried out at equivalence ratio 0.5 and pressure 10 bar, from 675 to 995 K. The targeted surrogate fuel is a mixture of toluene and n-heptane in order to capture the additive effect on both cool flame and main ignition.