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Technical Paper

Simulation of Fuel-Air Interaction in a Four Stroke Four Valve Direct Injected Spark Ignition (DISI) Engine

2007-04-16
2007-01-0153
Of late Direct Injection Spark Ignition (DISI) engines are replacing the carburetted SI engines due to certain inherent advantages like uniform distribution of fuel-air mixture in all cylinders in multi cylinder engines. However the homogeneity of the mixture depends on the time of injection as well as the type of fuel injector. It is expected that late in the compression stroke the fuel-air mixture near the spark plug should be a combustible mixture. In order to achieve this, proper air motion during induction and compression is a must. Further the interaction of fuel and air from the start of injection is equally important. This paper addresses these issues. For this a CFD study has been carried out. The injection timings selected are 90, 180 and 2700 aTDC, the idea being to understand the effects of early or late injection on fuel air mixing. The appropriate governing equations are solved using finite volume method. RNG k-ε turbulence model is used for physical modelling.
Technical Paper

Multi-Cycle LES Simulations of Flow and Combustion in a PFI SI 4-Valve Production Engine

2007-04-16
2007-01-0151
The LES technique has been applied to the simulation of 9 consecutive complete engine cycles of a single cylinder, spark-ignited 4valve engine. The simulations have been realized with the AVBP code, jointly developed by IFP and CERFACS. An extended coherent flame model approach (ECFM-LES) has been used to model spark ignition and turbulent combustion, and is shortly presented, along with the used turbulence models. The engine was fuelled with gaseous propane injected far upstream from the intake, so that fuel injection was not simulated, the fresh charge being assumed to be homogeneous. After a description of the numerical set-up, results obtained with LES are compared with experimental findings on cycle to cycle cylinder pressure evolutions. It is shown that LES indeed captures qualitatively the observed cyclic variability of the engine, even with only 9 cycles simulated.
Technical Paper

Multidimensional Cycle Analysis on a Novel 2-Stroke HSDI Diesel Engine

2007-04-16
2007-01-0161
The Department of Mechanical and Civil Engineering (DIMeC) of the University of Modena and Reggio Emilia is developing a new type of small capacity HSDI 2-Stroke Diesel engine, featuring a specifically designed combustion system. The present paper is focused on the analysis of the scavenging process, carried out by means of 3D-CFD simulations, supported by 1D engine cycle calculations. First, a characterization of the flow through the ports and within the cylinder is performed under conventional operating conditions. Then, a complete 3D cycle simulation, including combustion, is carried out at four actual operating conditions, at full load. The CFD results provide fundamental information to address the development of the scavenging system, as well as to calibrate a comprehensive 1D engine model.
Technical Paper

Combustion Modeling of Diesel Combustion with Partially Premixed Conditions

2007-04-16
2007-01-0163
Two turbulent combustion modeling approaches, which were large eddy simulations in conjunction with detailed kinetics (LES-CHEMKIN) and Reynolds Averaged Navier Stokes with detailed kinetics (RANS-CHEMKIN), were used to model two partially premixed engine conditions. The results were compared with average pressure and heat release data, as well as images of in-cylinder ignition chemiluminescence and OH radical distributions. Both LES-CHEMKIN and RANS-CHEMKIN match well with experimental average data. However, LES-CHEMKIN has advantages over RANS-CHEMKIN in predicting the details of location of ignition sites, temperature as well as OH radical distributions. Therefore, LES offers more realistic representations of the combustion process. As a further improvement aiming at saving computational cost and accounting for turbulence-chemistry interactions, a flamelet time scale (FTS) combustion model is coupled with CHEMKIN to predict the entire combustion process. In this new approach (i.e.
Technical Paper

A CFD Study to Optimize the Injection Strategy for Diesel Particulate Filter Regeneration

2007-04-16
2007-01-0164
Diesel engines have been progressing a lot during recent years. Beside the driving pleasure due to high torque and the low fuel consumption, it is more and more important to reduce combustion noise and pollutant emissions such as smoke and NOx. The exhaust after-treatment systems, in particular Diesel Particulate Filter (DPF), have therefore become as a standard for Euro5 applications and for some of the heaviest vehicles for Euro4. The DPF requires periodic regenerations under high temperature conditions in order to burn out the soot cumulated inside. One of the simplest strategies consists of one or several late injections. Typically, retarding the main and adding an early post injection generate high exhaust temperature while a very late one with a suitable quantity provides hydrocarbons, which burn inside the Diesel Oxidation Catalyst (DOC), and ensures the required temperature upstream the DPF.
Technical Paper

Effects of Average Driving Cycle Speed on Lean-Burn Natural Gas Bus Emissions and Fuel Economy

2007-01-23
2007-01-0054
Although diesel engines still power most of the heavy-duty transit buses in the United States, many major cities are also operating fleets where a significant percentage of buses is powered by lean-burn natural gas engines. Emissions from these buses are often expressed in distance-specific units of grams per mile (g/mile) or grams per kilometer (g/km), but the driving cycle or route employed during emissions measurement has a strong influence on the reported results. A driving cycle that demands less energy per unit distance than others results in higher fuel economy and lower distance-specific oxides of nitrogen emissions. In addition to energy per unit distance, the degree to which the driving cycle is transient in nature can also affect emissions.
Technical Paper

Extinction of Methanol and Ethanol Flames in Premixed Flows

2007-01-23
2007-01-0057
Alcohols like methanol (CH3OH) and ethanol (C2H5OH) are well known alternative fuels. Ethanol, which replaced MTBE in California, is added to regular gasoline up to 5% without any modifications required to a normal gasoline engine. Recently E85, an ethanol-gasoline mixture of 85% ethanol and 15% gasoline derived from crude oil, got attention as an alternative fuel due to high gas prices and environmental acceptance. Therefore, it is important to understand the basics of alcohol combustion. Experimental and numerical studies are conducted on extinction of methanol and ethanol flames in premixed laminar flows. The studies are performed in a counter-flow configuration. The burner used in the experiments is made up of two opposing ducts. Two configurations are considered. In one configuration, a premixed reactant stream made up of vaporized fuel, air, and nitrogen is introduced from one duct and nitrogen from the other.
Technical Paper

Alcohol-Based Fuels in High Performance Engines

2007-01-23
2007-01-0056
The paper discusses the use of alcohol fuels in high performance pressure-charged engines such as are typical of the type being developed under the ‘downsizing’ banner. To illustrate this it reports modifications to a supercharged high-speed sports car engine to run on an ethanol-based fuel (ethanol containing 15% gasoline by volume, or ‘E85’). The ability for engines to be able to run on alcohol fuels may become very important in the future from both a global warming viewpoint and that of security of energy supply. Additionally, low-carbon-number alcohol fuels such as ethanol and methanol are attractive alternative fuels because, unlike gaseous fuels, they can be stored relatively easily and the amount of energy that can be contained in the vehicle fuel tank is relatively high (although still less than when using gasoline).
Technical Paper

Combustion and Smoke Emission Studies on a Hydrogen Fuel Supplemented DI Diesel Engine

2007-01-23
2007-01-0055
Hydrogen addition to ethylene and acetylene -air laminar diffusion flames has shown substantial reduction in soot formation. In the present study, hydrogen was carbureted in a single cylinder, naturally aspirated DI diesel engine, and combustion events and smoke emissions were studied. With hydrogen induction particularly when its energy share increased above 15%, contrary to the results reported by earlier investigators a sharp decrease in ignition delay (ID), very high peak pressure rates, increase in smoke and loss in fuel efficiency were observed. At hydrogen energy share of about 30%, ignition delay drops to nearly 0-1degree CA and peak rates of pressure rise to 25-30 bar/deg CA. Smoke emissions at low hydrogen induction rates reduced slightly but increased sharply above 15 to 20% hydrogen energy share.
Technical Paper

EGR and Intake Boost for Managing HCCI Low-Temperature Heat Release over Wide Ranges of Engine Speed

2007-01-23
2007-01-0051
Reaching for higher loads and improving combustion-phasing control are important challenges for HCCI research. Although HCCI engines can operate with a variety of fuels, recent research has shown that fuels with two-stage autoignition have some significant advantages for overcoming these challenges. Because the amount of low-temperature heat release (LTHR) is proportional to the local equivalence ratio (ϕ), fuel stratification can be used to adjust the combustion phasing (CA50) and/or burn duration using various fuel-injection strategies. Two-stage ignition fuels also allow stable combustion even for extensive combustion-phasing retard, which reduces the knocking propensity. Finally, the LTHR reduces the required intake temperature, which increases the inducted charge mass for a given intake pressure, allowing higher fueling rates before knocking and NOx emissions become a problem. However, the amount of LTHR is normally highly dependent on the engine speed.
Technical Paper

Formaldehyde and Hydroxyl Radicals in an HCCI Engine - Calculations and LIF-Measurements

2007-01-23
2007-01-0049
Concentrations of hydroxyl radicals and formaldehyde were calculated using homogeneous (HRM) and stochastic reactor models (SRM), and the result was compared to LIF-measurements from an optically accessed iso-octane / n-heptane fuelled homogeneous charge compression ignition (HCCI) engine. The comparison was at first conducted from averaged total concentrations / signal strengths over the entire combustion volume, which showed a good qualitative agreement between experiments and calculations. Time- and the calculation inlet temperature resolved concentrations of formaldehyde and hydroxyl radicals obtained through HRM are presented. Probability density plots (PDPs) through SRM calculations and LIF-measurements are presented and compared, showing a very good agreement considering their delicate and sensitive nature.
Technical Paper

Effect of Octane Rating and Charge Stratification on Combustion and Operating Range with DI PCCI Operation

2007-01-23
2007-01-0053
A single cylinder engine has been run with direct-injection premixed charge compression ignition (PCCI) operation. The operation is fueled with primary reference fuels for a wide variety of injection timing and equivalence ratio to investigate the effect of charge stratification and octane rating on PCCI combustion. The test results showed that although the change of the injection timing can gain the high combustion efficiency for a wide range of equivalence ratio, the combustion phasing where the high combustion efficiency is accomplished is not varied only by changing the injection timings. Therefore, the only change of injection timings does not improve the thermal efficiency which is influenced by the combustion phasing. On the other hand, at the fixed compression ratio, inlet air temperature and so on, the octane rating is useful in altering the combustion phasing.
Technical Paper

A Novel Strategy for Fast Catalyst Light-Off without the Use of an Air Pump

2007-01-23
2007-01-0044
A novel engine management strategy for achieving fast catalyst light-off without the use of an exhaust air pump in a port-fuel-injected, spark ignition engine was developed. A conventional 4-cylinder engine was operated with three cylinders running rich and the fourth one as an air pump to supply air to the exhaust manifold. Under steady-state cold coolant conditions, this strategy achieved near total oxidation of CO and HC with sufficiently retarded spark timing, resulting in a 400% increase in feedgas enthalpy flow and a 90% reduction in feedgas HC emissions compared to conventional operation. The strategy was also evaluated for crank starts. Using the existing engine hardware, implementing the strategy resulted in a reduction in catalyst light-off time from 28.0 seconds under conventional operation to 9.1 seconds.
Technical Paper

The Application of an Enhanced Ignition Delay Model to HCCI Engines and Comparison to Engine Measurements

2007-01-23
2007-01-0048
The paper describes the application of an enhanced ignition delay model, developed by Yates and co-workers, to the operation of a single cylinder HCCI engine. The ignition delay description was further expanded in this paper to incorporate the effects of air-fuel ratio changes (to cater for lean operation) and residual exhaust gas. Variable combustion (heat release) duration was added, yielding improvement on the common assumption of a fixed duration. The model was compared to measurement performed in a variable compression ratio, single cylinder Ricardo E6 engine and the paper details the engine preparation, test procedure and results. A variety of fuels were tested and modelled and results for two fuels (n-heptane and methanol) were presented in the paper. These two fuels represent extremes of autoignition resistance (with octane numbers of 0 and 106, respectively).
Technical Paper

CNG/Methane-Combustion in a Homogeneous-Combustion Radical-Ignition D.I. Diesel Engine

2007-01-23
2007-01-0047
A detailed examination is made of the effects of internally generated “radicals” on the chemical-kinetics mechanism for CNG (compressed natural gas) combustion in a direct-injection (DI) diesel engine operating under ultra-lean fuel conditions at normal diesel compression ratios. The primary generating site for these “radical” chemical species is a set of mini-chambers located within the cylinder head. Explored in this study is the potential for controlling the autoignition timing of the engine by altering the rates of this radical generation process via the temperature management of these chambers. The study suggests that the temperature management of these secondary chambers may help enable the control of the ignition timings in response to engine load changes.
Technical Paper

Advanced Diesel Particulate Filter Design for Lifetime Pressure Drop Solution in Light Duty Applications

2007-01-23
2007-01-0042
Highly efficient wall-flow diesel particulate filters (DPF) are the primary means of PM emissions control in light-duty diesel vehicles. The successful commercialization of DPF technology has allowed combining attractive characteristics (good fuel economy, high low-end torque characteristics) of a diesel engine with significant PM emissions reductions to meet the stringent legislation. The design for advanced filter systems is driven by the lifetime pressure drop requirements with the accumulation of non-combustible materials (ashes) over time in the filter. More compact filter designs can be achieved by using filters with the proprietary Asymmetric Cell Technology (ACT) providing a larger inlet channel volume and therefore a higher ash storage capacity in the same space envelope without compromising the filter bulk heat capacity and mechanical integrity.
Technical Paper

Optimum Diesel Fuel for Future Clean Diesel Engines

2007-01-23
2007-01-0035
Over the next decades to come, fossil fuel powered Internal Combustion Engines (ICE) will still constitute the major powertrains for land transport. Therefore, their impact on the global and local pollution and on the use of natural resources should be minimized. To this end, an extensive fundamental and practical study was performed to evaluate the potential benefits of simultaneously co-optimizing the system fuel-and-engine using diesel as an example. It will be clearly shown that the still unused co-optimizing of the system fuel-and-engine (including advanced exhaust after-treatment) as a single entity is a must for enabling cleaner future road transport by cleaner fuels since there are large, still unexploited potentials for improvements in road fuels which will provide major reductions in pollutant emissions both in vehicles already in the field and even more so in future dedicated vehicles.
Technical Paper

Exploitation of Energy Resources and Future Automotive Fuels

2007-01-23
2007-01-0034
The future exploitation of global energy resources is currently being hotly debated by politicians and by sections of the scientific community but there is little guidance available in the engineering literature as to the full gamut of options or their viability with respect to fuelling the world's vehicles. In the automotive industry extensive research is being undertaken on the use of alternative fuels in internal combustion engines and on the development of alternative powerplants but often the long-term strategy and sustainability of the energy sources to produce these fuels is not clearly enunciated. The requirement to reduce CO2 emissions in the face of accelerating global warming scenarios and the depletion of fossil-fuel resources has led to the widespread assumption that some form of ‘hydrogen economy’ will prevail; this view is seldom justified or challenged.
Technical Paper

An Experimental Investigation of Fischer-Tropsch Fuels in a Light-Duty Diesel Engine

2007-01-23
2007-01-0030
Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.
Technical Paper

An Accurate Determination of the Cetane Number Value of GTL Diesel

2007-01-23
2007-01-0026
A method for determining the exceptionally high cetane number value of SasolChevron GTL diesel is described. The conventional ASTM D613 method is inadequate at such high cetane number ratings where the reproducibility exceeds ± 8 numbers. The ignition delay of a selection of primary and secondary reference fuels were modeled and characterized using a combustion bomb apparatus and this information was used to calibrate a virtual cetane engine model. CFD simulations of the combustion bomb apparatus was used to validate the calculation process using n-heptane as the reference fuel. The analytical treatment was applied to Sasol GTL diesel and the cetane number was deduced as 86.9 with a 95% confidence interval of ±1.3.
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