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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.

A 3 way catalytic converter (3WCC) model based on a global kinetic model was developed and validated against laboratory scale and engine test bench experiments. Various equivalence ratios and temperatures were tested. A methodology was finalized and applied to calibrate the kinetic constants. Laboratory scale experiments were first used to characterize the reaction mechanism during light-off, including the way reduction and oxidation reactions begin and compete with each other when temperature increases. The numerical results are in good agreement with the laboratory scale light-off results. Also, when adapted to simulate the engine test bench experiments, the model is able to correctly reproduce both the light-off tests and the 3WCC conversion efficiency evolution versus equivalence ratio. A calibration method in two steps was thus established and successfully used. The combination of modeling with experimental work appeared to be a powerful tool to determine the reaction mechanism.

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.

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.

The model presented in this paper is an original contribution for two main mechanisms involved in a Diesel combustion chamber: the micro-mixing and the combustion heat release. The micro-mixing phenomenon is modelled thanks to the presumed probability density function theory adapted to the 0D combustion modeling issues in order to take into account the stratification of air / fuel ratio around the spray. The combustion heat release is obtained from complex chemistry look-up tables. These tables are issued from a dedicated use of the Flame Prolongation of ILDM theory and allow a large range of combustion conditions since it includes high EGR rates. Moreover, the spray model including evaporation and turbulent macro-mixing is based on the well-known Siebers theory.

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.

Future emissions standards for passenger cars require a reduction of NOx (nitrogen oxide) and CO₂ (carbon dioxide) emissions of diesel engines. One of the ways to reach this challenge while keeping other emissions under control (CO: carbon monoxide, HC: unburned hydrocarbons and particulates) is to reduce the volumetric compression ratio (CR). Nevertheless complications appear with this CR reduction, notably during very cold operation: start and idle. These complications justify intensifying the work in this area. Investigations were led on a real 4-cylinder diesel 13.7:1 CR engine, using complementary tools: experimental tests, in-cylinder visualizations and CFD (Computational Fluid Dynamics) calculations. In previous papers, the way the Main combustion takes place according to Pilot combustion behavior was highlighted. This paper, presents an in-depth study of mixture preparation and the subsequent combustion process.

For studying simultaneously and early in the development process the effects of engine design parameters and of control strategies on HC emissions, a methodology has been set up to reproduce on a gasoline single-cylinder engine the beginning of MVEG cycle. This methodology uses different fuels and analysis tools to assess the HC sources. Oil and water are heated to follow the thermal behavior of a multi cylinder engine. A fast prototyping system is used to control the engine. Special attention has been paid to take into account the acoustic effect on the air feeding. The main tendencies observed in stabilized conditions are similar to transient test conditions with GDI engine. Wall wetting appears as the main source of HC emission in case of direct injection. Transient effects are especially sensitive during cold conditions.

With a high thermal efficiency and low CO2 (carbon dioxide) emissions, Diesel engines become leader of transport market. However, the exhaust-gas legislation evolution leads to a drastic reduction of NOx (nitrogen oxide) standards with very low particulate, HC (unburned hydrocarbons) and CO (carbon monoxide) emissions, while combustion noise and fuel consumption must be kept under control. The reduction of the volumetric compression ratio (CR) is a key factor to reach this challenge, but it is today limited by the capabilities to provide acceptable performances during very cold operation: start and idle below −10°C. This paper focuses on the understanding of the main parameter’s impacts on cold operation. Effects of parameters like hardware configuration and calibration optimization are investigated on a real 4 cylinder Diesel 14:1 CR engine, with a combination of specific advanced tools.

Future emission standards for Diesel engine will require a drastic reduction of engine-out NOx emissions with very low level of particulate matter (PM), HC and CO, and keeping under control fuel consumption and combustion noise. One of the most promising way to reach this challenge is to reduce compression ratio (CR). A stringent limitation of reducing Diesel CR is currently cold start requirements. Indeed, reduction of ambient temperature leads to penalties in fuel vaporization and auto ignition capabilities, even more at very low temperature (-20°C and below). In this paper, we present the work operated on an HSDI Common rail Diesel 4-cyl engine in three area: engine tests till very low temperature (down to -25°C); in cylinder imaging (videoscope) and CFD code development for cold start operation. First, combustion chamber is adapted in order to reach low compression ratio (CR 13.7:1).

Faced with the need to reduce greenhouse gas emissions, diesel engines present the advantage of having low CO₂ emission levels compared to spark-ignited engines. Nevertheless, diesel engines still suffer from the fact that they emit pollutants and, particularly nitrogen oxides (NOx) and particulates (PM). One of the most promising ways to meet this challenge is to reduce the compression ratio (CR). However a current limitation in reducing the diesel CR is cold start requirements. In this context, the fuel characteristics such as the cetane number, which represents ignition, and volatility could impact cold start. That is why a matrix of 8 fuels was tested. The cetane number ranges from 47.3 to 70.9 and the volatility, represented by the temperature necessary to distillate 5% of the product (T5%), ranges from 173 to 198°C. The engine tests were carried out at -25°C, on a common rail 4-cylinder diesel engine.

Soot models applied to Diesel combustion can be grouped into two classes, one based on the flamelet concept and the other based on the homogeneous reactor concept. The first assumes that the laminar diffusion flame structure of the reaction zone, in the mixture fraction space, is preserved while convected and strained by the turbulent flow. The second assumes that the properties of the reaction zone are locally homogeneous. Thus the aerodynamic and chemical reaction interactions are modeled with opposing assumptions: the first assumes fast chemistry, the second fast mixing. In this work, we first compare results obtained with a flamelet library approach to those with a homogeneous reactor approach. Recognizing that both types of models apply in different regions of Diesel combustion, we then propose a new approach for soot modeling in which they are coupled.

Electrical Low Pressure Impactor (ELPI) is often employed to measure the particle number and size distribution of internal combustion engines exhaust gas. If appropriate values of particle density are available, the particle mass can be estimated by this method. Exhaust particles of three Euro3 passenger cars (one gasoline operating under stoichiometric conditions, one Diesel and one Diesel equipped with Diesel Particulate Filter) are measured using the current European regulations (gravimetric method on the are New European Driving Cycle) and estimated by ELPI particle number and size distribution. Different values for particle density are used to estimate the particle mass using all ELPI stages or only some of them. The results show that the particle mass estimated by ELPI is well correlated with the mass determined by filters for PM emissions higher than 0.025 g/km. This correlation is not very good at lower emissions.

To ensure overall optimisation of heavy duty engine performance (with the respect of NOx&PM future European and US emissions standards), the use of a high efficiency NOx after-treatment system such as a NOx trap appears to be necessary. But running in rich conditions, even for a short time, leads to a large increase of particulate emissions so that a particulate filter is required. A first investigation with a NOx-trap only has been carried out to evaluate and optimise the storage, destorage and reduction phases from the NOx conversion efficiency and fuel penalty trade-off. The equivalence ratio level, the fuel penalty and the temperature level of the NOx-trap have been shown as a key parameter. Respective DPF and LNA locations have been studied. The configuration with the NOx-trap upstream provides the best NOx / fuel penalty trade-off since it allows NOx slip reduction and does not disturb the rich pulses.

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.

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).

The Particulate Measurement Programme (PMP) works on the identification of a method to replace or complete the existing particle mass (PM) measurement method. The French PMP subgroup, composed by IFP, PSA Peugeot-Citroën, Renault and UTAC, proposes an improved gravimetric method for the measurement of emitted particles, and conducted an inter-laboratory test to evaluate its performances. The technical programme is based on tests carried out on a Euro3 Diesel passenger car (PC), tested on the New European Driving Cycle (NEDC). To achieve low particulate matter (PM) emissions, the EGR is disconnected and a paraffinic fuel is used. The regulated pollutants are also measured. It is shown that the multiple filter weighing and a 0.1 μg balance instead of a 1 μg one are not necessary, as the first weighing and the 1 μg balance performances are satisfactory for type-approval purposes.

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.