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Technical Paper

Improving Emissions, Noise and Fuel Economy Trade-Off by using Multiple Injection Strategies in Diesel Low Temperature Combustion (LTC) Mode

2010-10-25
2010-01-2162
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.
Journal Article

Effects of Methane/Hydrogen Blends On Engine Operation: Experimental And Numerical Investigation of Different Combustion Modes

2010-10-25
2010-01-2165
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.
Technical Paper

Development of a Flex Fuel Vehicle: Impact on Powertrain's Design and Calibration

2010-10-25
2010-01-2087
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.
Journal Article

Cold Start on Diesel Engines: Effect of Fuel Characteristics

2010-05-05
2010-01-1506
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.
Journal Article

Increasing Power Density in HSDI Engines as an Approach for Engine Downsizing

2010-05-05
2010-01-1472
In the context of CO₂ emission regulations and increase of energy prices, the downsizing of engine displacement is a widely discussed solution that allows a reduction of fuel consumption. However, high power density is required in order to maintain the power output and a good driveability. This study demonstrates the potential to strongly increase the specific power of High Speed Diesel Injection (HSDI) diesel engines. It includes the technological requirements to achieve high specific power and the optimal combination of engine settings to maximize specific power. The results are based on experimental work performed with a prototype single-cylinder engine (compression ratio of 14). Tests were conducted at full load, 4000 rpm. Part load requirements are also taken into account in the engine definition to be compatible with the targets of new emission standards.
Journal Article

Optimization of a Euro 5 Vehicle Powered by an Ethanol Based Diesel Fuel

2010-05-05
2010-01-1520
Diversifying energy resources and reducing greenhouse gas emissions are key priorities in the forthcoming years for the automotive industry. Currently, among the different solutions, sustainable biofuels are considered as one of the most attractive answer to these issues. This paper deals with the vehicle application of an innovative diesel fuel formulation using Ethanol to tackle these future challenges. The main goal is to better understand the impact of using biofuel blends on engine behavior, reliability and pollutants emissions. This alternative oxygenated fuel reduces dramatically particulate matter (PM) emissions; this paves the way to improve the NOx/PM/CO₂ trade-off. Another major interest is to avoid adding a particulate filter in the exhaust line and to avoid modifying powertrain and vehicle hardware and therefore to minimize the overall cost to fulfill upcoming emission regulations.
Journal Article

Towards an Innovative Combination of Natural Gas and Liquid Fuel Injection in Spark Ignition Engines

2010-05-05
2010-01-1513
In order to address the CO₂ emissions issue and to diversify the energy for transportation, CNG (Compressed Natural Gas) is considered as one of the most promising alternative fuels given its high octane number. However, gaseous injection decreases volumetric efficiency, impacting directly the maximal torque through a reduction of the cylinder fill-up. To overcome this drawback, both independent natural gas and gasoline indirect injection systems with dedicated engine control were fitted on a RENAULT 2.0L turbocharged SI (Spark Ignition) engine and were adapted for simultaneous operation. The main objective of this innovative combination of gas and liquid fuel injections is to increase the volumetric efficiency without losing the high knocking resistance of methane.
Technical Paper

Modeling the Laminar Flame Speed of Natural Gas and Gasoline Surrogates

2010-04-12
2010-01-0546
An unified model with a single set of kinetic parameters has been proposed for modeling laminar flame velocities of several alkanes using detailed kinetic mechanisms automatically generated by the EXGAS software. The validations were based on recent data of the literature. The studied compounds are methane, ethane, propane, n-butane, n-pentane, n-heptane, iso-octane, and two mixtures for natural gas and surrogate gasoline fuel. Investigated conditions are the following: unburned gases temperature was varied from 300 to 600 K, pressures from 0.5 to 25 bar, and equivalence ratios range from 0.4 to 2. For the overall studied compounds, the agreement between measured and predicted laminar burning velocities is quite good.
Technical Paper

Quantifying Benefits of Dual Cam Phasers, Lean Mixture and EGR on the Operating Range and Fuel Economy of a PFI NVO CAI Engine

2010-04-12
2010-01-0844
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.
Technical Paper

Control-Oriented Mean-Value Model of a Fuel-Flexible Turbocharged Spark Ignition Engine

2010-04-12
2010-01-0937
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.
Technical Paper

Matching and Evaluating Methods for Euro 6 and Efficient Two-stage Turbocharging Diesel Engine

2010-04-12
2010-01-1229
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.
Technical Paper

Simulation of Urea-SCR Process Applied to Lean-burn SI Engines

2009-11-02
2009-01-2776
Lean-burn combustion in SI engines can significantly reduce fuel consumption but NOx reduction becomes challenging because classic three-way catalyst (TWC) is no more efficient. Urea-SCR is then an interesting alternative solution because of its high NOx conversion efficiency without any additional fuel consumption. The coupling between two SI lean-burn engines (stratified and homogeneous combustion) and a urea-SCR catalyst was simulated on the NEDC cycle. Simulation results showed that the SCR efficiency would comply with the limits required by future Euro 5/6 regulations. Associated urea solution consumptions were estimated thanks to a simplified model. Finally, a comparison with a Diesel application was also made. It showed that the required amount of reducing agent remained significantly higher for SI lean-burn engines than for Diesel engine.
Journal Article

Cold Operation with Optical and Numerical Investigations on a Low Compression Ratio Diesel Engine

2009-11-02
2009-01-2714
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.
Technical Paper

Optimal Design for a Highly Downsized Gasoline Engine

2009-06-15
2009-01-1794
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.
Technical Paper

Ethanol as a Diesel Base Fuel: Managing the Flash Point Issue - Consequences on Engine Behavior

2009-06-15
2009-01-1807
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.
Journal Article

A Comparison of Combustion and Emissions Behaviour in Optical and Metal Single-Cylinder Diesel Engines

2009-06-15
2009-01-1963
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.
Journal Article

Development of Specific Tools for Analysis and Quantification of Pre-ignition in a Boosted SI Engine

2009-06-15
2009-01-1795
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.
Journal Article

Online Implementation of an Optimal Supervisory Control for a Parallel Hybrid Powertrain

2009-06-15
2009-01-1868
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).
Journal Article

Advanced Injection Strategies for Controlling Low-Temperature Diesel Combustion and Emissions

2009-06-15
2009-01-1962
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.
Technical Paper

Generating Thermal Conditions to Regenerate a DPF: Impact of the Reductant on the Performances of Diesel Oxidation Catalysts

2009-04-20
2009-01-1085
The influence of the type of fuel and the feeding means to a DOC, in order to regenerate a DPF, was investigated. Diesel fuel in cylinder late post-injection was compared to the injection in the exhaust line, through an exhaust port injector, of diesel fuel, B10 (diesel fuel containing 10% of esters) and gasoline. Diesel fuel exhaust injection resulted in a deteriorated conversion efficiency, while the incorporation of esters to the diesel fuel was demonstrated to have no influence. Gasoline exhaust injection led to less HC slip than diesel fuels. Temperature dynamics resulting from injection steps showed taught that the shorter the hydrocarbons (within the tested fuels), the slower the response. These differences can be caught by simple models, leading to interesting opportunities for the model-based control of the DPF inlet temperature during active regenerations.
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