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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.

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.

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.

KIFP, an hexahedral unstructured version of KIVA-MB (KMB), the current CFD code for engines at IFP, has been developed. Based on KIVA algorithms (finite volume on staggered grids, time-splitting, SIMPLE loop, sub-cycled advection…), the new solver has been built step by step with a strong control on the numerical results. This paper shows the different phases of this work. The numerical approaches and developments are discussed. Several moving grids algorithms have been tested without the flow and results are presented. The flow with its physical properties has been implemented step by step. Some academic examples are shown and compared with KMB or analytical results, like scalar advection or multi-species diffusion. Better precision and convergence in the physical fields are observed. Iterative loops and advective sub-cycles are also reduced thanks to the unstructured formalism. Super-scalar machines being widely used and developed, KIFP is dedicated for them.

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.

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.

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.

Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. For this paper, we describe results from comparative studies using constant-volume vessels at Sandia National Laboratories and IFP.

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.

The paper discusses different alternative choices regarding the simulation and control of combined hybrid vehicles with a simple or compound power split device (PSD). These choices concern the causal representation of PSD both in a vehicle model and in the supervisory controller, the structure of the supervisory controller, and the pathway to generate the setpoints to the component-level controllers. Quasistatic and high-frequency simulations provide the example applications to assess the competing approaches.

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.

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.

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 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.

Three dimensional CFD tools are commonly used to simulate spray injection and combustion in DI Diesel engines. However typical computations are strongly mesh dependent. By now it is not possible to enhance grid resolution since it would violate the underlying assumptions for the Lagrangian liquid phase description. Besides, a full Eulerian approach with an adapted mesh is not practical at the moment mainly because of prohibitive computer requirements. Based on the Lagrangian-Eulerian approach, new approaches have been developed: the Coupled Lagrangian-Eulerian (CLE) model for the two-way coupling between the spray and the air flow and a new combustion model (CFM3Z) which allows a description of the fuel-oxidizer sub-grid mixing. The previously introduced CLE model consists in retaining vapor and momentum along parcel trajectories as long as the mesh is insufficient to resolve the steep gradients created by the spray.