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Technical Paper

Effect of Nozzle Diameter and EGR Ratio on the Flame Temperature and Soot Formation for Various Fuels

2001-05-07
2001-01-1939
In this study, effects of nozzle hole diameter and EGR ratio on flame temperature (indication of NO formation) and KL value (indication of soot formation) were investigated. Combustion of a single diesel fuel spray in the cylinder of a rapid compression machine (RCM) was analyzed. Three nozzles with different hole diameter were used corresponding to present, near term and long term heavy duty diesel engine specifications. EGR was simulated through 2%vol. CO2 addition to the inlet air and by increase of in-cylinder surrounding gas temperature. Various types of fuels were used in this. The ignition and combustion processes of diesel fuel spray were observed by a high-speed direct photography and by indicated pressure diagrams. Flame temperature and KL factor were analyzed by a two-color method. With larger nozzle hole diameters there are larger high temperature areas. With smaller nozzle hole diameters there is more soot formed. Introduction of 2% vol.
Technical Paper

Effects of Aromatics Content and 90% Distillation Temperature of Diesel Fuels on Flame Temperature and Soot Formation

2001-05-07
2001-01-1940
In this study, the effects of fuel properties, aromatics content and 90% distillation temperature T90, on flame temperature and soot formation were studied using a rapid compression machine (RCM). Aromatics content and T90 distillation temperature were parameters isolated from influence of each other, and from cetane number. A fuel spray was injected in the RCM combustion chamber by a single nozzle hole. The ignition and combustion processes of diesel spray were observed by a high-speed direct photography. Flame temperature and KL factor (which indicates the soot concentration), were analyzed by the two-color method. The rate of heat release was analyzed from indicated diagrams. The fuels with aromatics content showed higher flame temperature. The fuel with highest T90 distillation temperature showed highest flame temperature.
Technical Paper

Analysis of DME Homogeneous Charge Compression Ignition Combustion

2003-05-19
2003-01-1825
The characteristics of auto-ignition of DME/Air mixture in Homogeneous Charge Compression Ignition (HCCI) engine were investigated by numerical calculation with elementary reactions and experiment. Calculations were carried out using Di-Methyl Ether (DME) elementary reactions at 0 dimension and adiabatic condition. DME is paid attention as the alternative fuel of next generation because of its possibility to take the place of conventional fossil fuels. DME has good characteristics of auto-ignition and combustion with low flame temperature, and makes no soot because of its molecular structure. In autoignition process, DME shows two-stage combustion, heat release with low temperature reaction (LTR) and high temperature reaction (HTR). This characteristic is similar to higher hydrocarbons such as gasoline in auto-ignition process. In this study, analysis of HCCI combustion of DME/Air mixture was carried out by using numerical calculation and comparing with experimental results.
Technical Paper

Numerical Analysis of Auto Ignition and Combustion of n-Butane and Air Mixture in the Homogeneous Charge Compression Ignition Engine by Using Elementary Reactions

2003-03-03
2003-01-1090
The combustion mechanism of the homogeneous charge compression ignition (HCCI) engine has been investigated by numerical calculations. Calculations were carried out using n-butane/air elementary reactions at 0 dimension and adiabatic condition to simplify the understanding of chemical reaction mechanisms in the HCCI engine without complexities of walls, crevices, and mixture inhomogeneities. n-Butane is the fuel with the smallest carbon number in the alkane family that shows two-stage auto-ignition, heat release with low temperature reaction (LTR) and high temperature reaction (HTR), similar to higher hydrocarbons such as gasoline at HCCI combustion. The CHEMKIN II code, SENKIN and kojima's n-butane elementary reaction scheme were used for the calculations. This paper consists of three main topics. First, the heat release mechanisms of the HCCI engine were investigated. The results show that heat release with LTR is HCHO oxidation reactions.
Technical Paper

Combustion Analysis of Natural Gas in a Four Stroke HCCI Engine Using Experiment and Elementary Reactions Calculation

2003-03-03
2003-01-1089
Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion regime in terms of high thermal efficiency and low emissions. It is difficult to control autoignition and combustion because they are controlled primarily by the chemical kinetics of air/fuel mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a four-stroke HCCI engine using experiment and elementary reactions calculation. The influence of equivalence ratio, intake temperature, intake pressure and engine speed on autoignition timing, autoignition temperature, combustion duration and the emissions of THC, CO, CO2 were investigated. And also, to clarify the influence of n-butane on autoignition and combustion of natural gas, it was changed the blend ratio of n-butane from 0 mol% to 10 mol% in methane / n-butane / air mixtures.
Technical Paper

Effects of High-Pressure Fuel Injection and a Micro-Hole Nozzle on Combustion in a Rapid Compression Machine

1997-02-24
970893
High pressure fuel injection and a micro-hole nozzle were used with a rapid compression machine to study soot and nitrogen oxide reduction by creating a uniform and lean fuel distribution in the combustion chamber. The rapid compression machine was optically accessible, which allowed high-speed photography and subsequent two-color flame temperature and soot concentration measurements to be made. In addition, band spectrum radical luminescence images were also observed.
Technical Paper

Alternative Fuels and Homogeneous Charge Compression Ignition Combustion Technology

1997-10-27
978449
Homogeneous charge compression ignition (HCCI) combustion requires high EGR rate and high intake temperature. HCCI combustion has not yet been made to operate at conditions other than low speed and low load in a four-stroke engine. Two stroke engine, however, have produced reasonable power in the HCCI combustion or active thermo-atmosphere combustion (ATAC) mode. In this paper, the nature of ATAC is discussed by spectroscopic observation to determine why the ATAC (under favorable condition) produces very low cyclic irregularity and low NO emission. ATAC low heat rejection engine and ATAC with alternative fuels are discussed.
Technical Paper

A Study on Adaptability of Alternative Fuels for Lean Burn Two-Stroke ATAC Engine

1997-10-27
978472
ATAC is “bulk-like” and/or “non-propagating” combustion caused by compression autoignition of premixture, and it is stable even in the lean region. And ATAC engine is expected to be an engine using alternative fuels which are difficult to apply to usual engines because of their low cetane number. In this study, a two-stroke ATAC engine test was carried out to evaluate an adaptability of alternative fuels for lean burn. Methanol, ethanol, DME, methane and propane were used as the test fuels, and the influence of fuel characteristics on autoignition timing, combustion duration and autoignition temperature were investigated in the lean region. Using oxygenated fuels, the lean limit of ATAC operation region shifts to lean side. ATAC autoignition temperature is not depend on equivalence ratio, delivery ratio and engine speed, and it is only decided by the kind of fuel. The order of the ATAC autoignition temperature is methanol, ethanol, DME, gasoline from lower side.
Technical Paper

Combustion Analysis of Methanol-Fueled Active Thermo-Atmosphere Combustion (ATAC) Engine Using a Spectroscopic Observation

1994-03-01
940684
To analyze the combustion mechanism of the so-called Active Thermo-Atmosphere Combustion (ATAC) in a two-stroke S.I. engine, a measuring system to obtain images of radical luminescence in the combustion chamber was developed. The ATAC engine tested was equipped with a quartz windows as the cylinder head. The instantaneous luminescence from radical species was observed using an image intensifier with a single band pass filter for both conventional and ATAC operating conditions. At ATAC operation, emissions from OH radicals were observed before heat release began, and after that, emissions from CH were observed. It was found that the ignition was initiated over the entire area of the combustion chamber and “bulk-like” and/or “non propagating” combustion occurred during ATAC engine operation.
Technical Paper

Experimental Study of Transient Gas Jet Impinging on a Wall

1990-02-01
900479
The process of forming mixtures of injected fuels and ambient air has significant effects on the ignition and combustion process in the direct injection engine. In these engines fuel is injected intermittently and fuel jet impinges on a combustion chamber wall. This study deals with a fundamental experiment on the mixing process of the transient gas jet together with the instantaneous concentration measurement and statistical analysis of the transient turbulent mixing process in the jet. Helium or carbon dioxide is injected at constant pressure into quiescent atmosphere through the single shot device. This paper presents a laboratory automation system for measuring the characteristics of transient gas jet and processing the data. A discussion on the process of mixture formation of transient gas jets impinging on a wall is carried out with time- and space- resolved concentration distribution.
Technical Paper

Surrounding Gas Effects on Soot Formation and Extinction - Observation of Diesel Spray Combustion Using a Rapid Compression Machine

1993-03-01
930603
A single action rapid compression machine was developed to observe the soot formation and oxidation processes in a diesel spray flame. Two color method was applied to analyze the flame temperature and KL factor from the flame image taken by high speed camera. Variation in gas oxygen concentration of the surrounding gas was achieved by adding different quantities of pure oxygen, nitrogen, carbon dioxide and argon gases to charged air within a range from 17 to 25 vol.% oxygen to examine the effects of the surrounding gas composition and the temperature, and of the flame temperature on soot formation and extinction. The initial gas temperature has much effect not only on the ignition but on soot formation speed. The higher oxygen concentration gives the higher flame temperature and the faster soot oxidation rate in the flame. Carbon dioxide has a soot reduction effect in spite of its lower flame temperature.
Technical Paper

Effects of Intake Oxygen Concentration on the Characteristics of Particulate Emissions from a D.I. Diesel Engine

1986-09-01
861233
The concept of oxygen enriched charging (OEC) was exploratively examined as a means of reducing particulate emissions from a direct injection (DI) diesel engine. A single cylinder DI engine was operated with intake gas oxygen concentrations of 21% to 29%, under a constant engine speed of 40 Hz, and several load conditions. It was found that OEC reduces particulate emissions from a DI diesel engine for all operating conditions tested. Insoluble particulate is especially suppressed by OEC at high load conditions. Oxygen enriched charging has little effect on particulate size distribution at high loads when the mass fraction of extractables is low. Fuel consumption, at constant injection timing, is improved a little by OEC. Emissions of NOx increase exponentially with increasing oxygen concentration. Ignition delay is decreased by OEC and this allows injection timing to be retarded to reduce NOx emissions without increasing the specific fuel consumption.
Technical Paper

Study on Characteristics of Particulate Emissions from a Direct Injection Diesel Engine using a Freezing Method in Sampling Process

1984-09-01
841077
Reduction of particulate emissions from diesel engine is an important theme from the view point of air pollution. Experiments were carried out using a four-stroke single cylinder direct-injection diesel engine. A new method to measure diesel particulates has been developed. Particulates were sampled with a freezing method just behind an exhaust valve and examined through a scanning electron microscope. Shape and structure of particulates and the size distributions are measured under wide operating conditions obtained with above method. The total mass of particulate emissions was measured using a dilution tunnel sampling system. The heat release processes were analyzed using indicator diagrams and the relation between burning condition and particulate emissions were discussed, after systematic experiments under constant revolution speed of 2000 r/min for several load and injection timing conditions.
Technical Paper

Influence of Pilot Injection on Combustion Characteristics and Emissions in a DI Diesel Engine Fueled with Diesel and DME

2011-08-30
2011-01-1958
This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion characteristics and emissions (NOx, CO, THC and Smoke) in a single-cylinder DI diesel engine. Additionally, results from diesel injection are compared with those shown in dimethyl ether (DME) injection under the identical injection strategy to demonstrate the sensitivity of the combustion characteristics and emissions to changes of the fuel type. Two fuel injection systems are applied for this experiment due to the differences of fuel characteristic with regard to physical and chemical properties. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (-4°CA aTDC, -2°CA aTDC, TDC, 2°CA aTDC and 4°CA aTDC). It was found that pilot injection offers good potential to lower the heat-release rate with reduced pressure traces regardless of the dwell time between injections and fuel type.
Technical Paper

The Research about Thermal Stratification Effect on Pressure Rise Rate in Supercharged HCCI Engine based on Numerical Analysis

2009-11-03
2009-32-0141
The HCCI engine is a next generation engine, with high efficiency and low emissions. However a rate of pressure rise is a major limitation for high load range. Recently, we are able to reduce the rate of pressure rise using thermal stratification. Nevertheless, this was insufficient to produce high power. Without the higher equivalent ratio, one way to improve the power is to increase the intake boost pressure. It is suggested that the rate of pressure rise is reduced by thermal stratification and the power is increased by boost pressure at the same time. The objective of this work is to understand the characteristics of combustion, knock and emissions for using both thermal stratification and the boost pressure. The calculations are performed by CHEMKIN and modified SENKIN. As a result of increasing the boost pressure, a higher IMEP was attained while the rate of pressure rise increased only slightly in the HCCI with thermal stratification.
Technical Paper

An Investigation of the Potential of Thermal and Mixing Stratifications for Reducing Pressure Rise Rate on HCCI Combustion by using Rapid Compression Machine

2009-11-03
2009-32-0085
Thermal and mixing stratifications have been thought as one of the ways to avoid an excessive pressure rise on HCCI combustion. The purpose of this research is to investigate the potential of thermal and mixing stratifications for reducing PRR (Pressure Rise Rate) on HCCI combustion. The pre-mixture with thermal and mixing stratifications is charged in RCM (Rapid Compression Machine). After that, the pre-mixture is compressed and in that process, in-cylinder gas pressure and chemiluminescence images are obtained and analyzed. Furthermore, experimental results are compared with the computational results calculated by using multi-zone model for analyzing these mechanisms.
Technical Paper

Analysis of the combustion dispersion mechanism in HCCI Engine

2009-11-03
2009-32-0086
Delaying CA50(Crank Angle of 50% Heat Release) of the HCCI engine to expansion stroke can lead to high indicated thermal efficiency as well as the avoidance of knocking. However, this method could induce the problem of cycle variability. In this study, the cycle-to-cycle variation of a HCCI engine fueled with DME was investigated. Experimental parameters of each cycle, such as in-cylinder temperature, pressure and gas flow rate, were recorded by fast response system, and analyzed consequently. Moreover, the interdependency between the combustion and the performance parameters were evaluated.
Technical Paper

Mechanism Analysis of Influence of Engine Speed on HCCI Combustion by using Numerical Calculation

2009-11-03
2009-32-0087
In HCCI Engine, HCCI combustion characteristics come under the influence of change of compression speed corresponding to engine speed. The purpose of this study is to investigate mechanism of influence of engine speed on HCCI combustion characteristics by using numerical analysis. At first, the Influence of engine speed was showed. And then, In order to clarified the mechanism of influence of engine speed, results of kinetics computations were analyzed to investigate the elementary reaction path for heat release at transient temperatures by using contribution matrix.
Technical Paper

An Investigation of the Effects of Fuel Inhomogeneity on the Pressure Rise Rate in HCCI engine using Chemiluminescence Imaging

2010-09-28
2010-32-0097
Theoretically, homogeneous charge compression engines (HCCI) are able to grant a high thermal efficiency, as well as a low NOx and particulate emissions. This ability is mainly due to the combustion process, which, contrary to both Diesel and Gasoline engine, is homogeneous in time and space within the combustion chamber. But despite these advantages, the engine operating condition is limited by the narrow boundaries of misfire at low load and knocking at high load. For that matter, one of the numerous ways of overcoming knocking is to deliberately create fuel inhomogeneities within the combustion chamber, since it has proved to lengthen combustion duration and to drastically reduce maximum pressure rise rate (PRR). Nevertheless, though the global effects of fuel inhomogeneities on PRR have been studied, we lack information that explains this phenomenon.
Technical Paper

An Investigation on DME HCCI Engine about Combustion Phase Control using EGR Stratification by Numerical Analysis

2012-10-23
2012-32-0077
This work has been investigated the potential of in-cylinder EGR stratification for reducing the pressure rise rate of DME HCCI engines, and the coupling of both thermal stratification and fuel stratification. The numerical analyses were done by using five-zone version of CHEMKIN-II kinetics rate code, and kinetic mechanics for DME. The effects of inert components were used for the presence of EGR in calculation. Three cases of EGR stratification were tested on both thermal stratification and fuel stratification at the fixed initial temperature, pressure and fueling rate at BDC. In order to explore the appropriate stratification of EGR, EGR width was employed from zero to thirty percent. Firstly, EGR homogeneity case which means EGR width zero was examined. Secondly, EGR is located densely in hotter zone for combining with thermal stratification or in richer zone for a combination with fuel stratification. Lastly, the case was judged inversely with the second case.
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