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Technical Paper

An Investigation of Different Ported Fuel Injection Strategies and Thermal Stratification in HCCI Engines Using Chemiluminescence Imaging

2010-04-12
2010-01-0163
The purpose of this study was to gain a better understanding of the effects of port fuel injection strategies and thermal stratification on the HCCI combustion processes. Experiments were conducted in a single-cylinder HCCI engine modified with windows in the combustion chamber for optical access. Two-dimensional images of the chemiluminescence were captured using an intensified CCD camera in order to understand the spatial distribution of the combustion. N-heptane was used as the test fuel. The experimental data consisting of the in-cylinder pressure, heat release rate, chemiluminescence images all indicate that the different port fuel injection strategies result in different charge distributions in the combustion chamber, and thus affect the auto-ignition timing, chemiluminescence intensity, and combustion processes. Under higher intake temperature conditions, the injection strategies have less effect on the combustion processes due to improved mixing.
Technical Paper

Experimental and Modelling Investigations of the Gasoline Compression Ignition Combustion in Diesel Engine

2017-03-28
2017-01-0741
In this work the gasoline compression ignition (GCI) combustion characterized by both premixed gasoline port injection and gasoline direct injection in a single-cylinder diesel engine was investigated experimentally and computationally. In the experiment, the premixed ratio (PR), injection timing and exhaust gas recirculation (EGR) rate were varied with the pressure rise rate below 10 bar/crank angle. The experimental results showed that higher PR and earlier injection timing resulted in advanced combustion phasing and improved thermal efficiency, while the pressure rise rates and NOx emissions increased. Besides, a lowest ISFC of 176 g/kWh (corresponding to IMEP =7.24 bar) was obtained, and the soot emissions could be controlled below 0.6 FSN. Despite that NOx emission was effectively reduced with the increase of EGR, HC and CO emissions were high. However, it showed that GCI combustion of this work was sensitive to EGR, which may restrict its future practical application.
Technical Paper

Evaluation of Knock Intensity and Knock-Limited Thermal Efficiency of Different Combustion Chambers in Stoichiometric Operation LNG Engine

2019-04-02
2019-01-1137
Liquefied natural gas (LNG) engine could provide both reduced operating cost and reduction of greenhouse gas (GHG) emissions. Stoichiometric operation with EGR and the three-way catalyst has become a potential approach for commercial LNG engines to meet the Euro VI emissions legislation. In the current study, numerical investigations on the knocking tendency of several combustion chambers with different geometries and corresponding performances were conducted using CONVERGE CFD code with G-equation flame propagation model coupled with a reduced natural gas chemical kinetic mechanism. The results showed that the CFD modeling approach could predict the knock phenomenon in LNG engines reasonably well under different thermodynamic and flow field conditions.
Technical Paper

Effects on Charge Non-Uniformity on Diesel Heat Release Analysis

1986-10-01
861568
A new model that includes the effects of spatial non-uniformity for the heat release analysis of internal combustion engine data has been formulated. The model has a form similar to the simple single zone thermodynamic models if two effective values of the ratio of specific heats T are defined. These values, denoted by γV and γH in the model, are weighted spatial average values of Y, and are dependent on the structure of the flame. These values have been evaluated using a three-dimensional numerical simulation of diesel combustion. Then the model is applied to the heat release analysis of diesel combustion data from a Rapid Compression Machine. The results show that the calculated cumulative net heat release is significantly higher (17% in this case) than that calculated using a single zone model.
Technical Paper

Characteristics of HCCI Engine Operating in the Negative-Valve-Overlap Mode

2005-05-11
2005-01-2133
Characteristics of un-throttled HCCI engine using negative valve overlap were examined under steady state and step-load change operations. The analysis employed a combined heat release analysis of the pressure data and a cycle simulation with a 1D gas exchange model to extract the residual fraction and the compression temperature from the experimental data. The residual gas fraction decreased with increase in engine load; the compression temperature decreased correspondingly. Substantial pumping loss attributed to the heat transfer in the re-compression process and the gas exchange friction was observed. At “optimum” setting of the combustion phasing, the GIMEP was not sensitive to the cycle-to-cycle combustion phasing variation. Large step high-to-low change in load was found to be stable. The reverse, however, had combustion failure in the first cycle due to unfavorable compression temperature and residual gas fraction.
Technical Paper

Investigation of the Effects of Injection Timing on Thermo-Atmosphere Combustion of Methanol

2007-04-16
2007-01-0197
The effects of various injection timing of methanol on thermo-atmosphere combustion of methanol by port injection of dimethyl ether (DME) and direct injection of methanol were experimentally investigated. The experiment results show that, as injection timing is at 6 degree before TDC, the combustion process comprises three stages: low temperature heat release of DME, high temperature heat release of DME and diffusion combustion of methanol. As injection timing increases, premixed combustion proportion of methanol is increased and diffusion combustion proportion is decreased. As injection timing increases to 126 degree before TDC, diffusion combustion of methanol disappears. At this time, the combustion process shows typical two stages heat release of HCCI combustion. As injection timing increases, required DME rate is increased, combustion efficiency and indicated thermal efficiency all first increase and then decrease.
Technical Paper

An Investigation on the Effects of Fuel Chemistry and Engine Operating Conditions on HCCI Engine

2008-06-23
2008-01-1660
A HCCI engine has been run at different operating boundaries conditions with fuels of different RON and MON and different chemistries. The fuels include gasoline, PRF and the mixture of PRF and ethanol. Six operating boundaries conditions are considered, including different intake temperature (Tin), intake pressure (Pin) and engine speed. The experimental results show that, fuel chemistries have different effect on the combustion process at different operating conditions. It is found that CA50 (crank angle at 50% completion of heat release) shows no correlation with either RON or MON at some operating boundaries conditions, but correlates well with the Octane Index (OI) at all conditions. The higher the OI, the more the resistance to auto-ignition and the later is the heat release in the HCCI engine. The operating range is also correlation with the OI. The higher the OI, the higher IMEP can reach.
Technical Paper

Fuel Factors Affecting the High-Load Limit of a Temperature Stratified Controlled Auto-Ignition Engine

2014-04-01
2014-01-1287
Factors affecting the pressure rise rate, and consequently the high-load limit, in the sequential ignition of a homogeneous charge in a temperature gradient have been identified. The pressure rise rate decreases with an increase in the magnitude of the temperature gradient and an increase in the sensitivity of the constant volume ignition delay time to temperature. It increases with an increase in the intrinsic reaction rate (i.e., the reaction rate for a charge of uniform composition and temperature). Since the ignition delay time and the intrinsic reaction rate are directly related to fuel properties, the high-load limit is sensitive to fuel selection. The above three factors are used to explain the high-load limit obtained from a knock limited Controlled Auto-Ignition (CAI) engine with a homogeneous charge operating with three different fuels. The fuel comparisons are made with the engine operating at the same combustion phasing.
Technical Paper

A Numerical Investigation on Effects of Charge Stratification on HCCI Combustion

2007-10-29
2007-01-4132
A fully coupled multi-dimensional CFD and reduced chemical kinetics model is adopted to investigate the effects of charge stratification on HCCI combustion and emissions. Seven different kinds of imposed stratification have been introduced according to the position of the maximal local fuel/air equivalence ratio in the cylinder at intake valve close. The results show that: The charge stratification results in stratification of the in-cylinder temperature. The former four kinds of stratification, whose maximal local equivalence ratios at intake valve close locate between the cylinder center and half of the cylinder radius, advance ignition timing, reduce the pressure-rise rate, and retard combustion-phasing. But the following three kinds of stratification, whose maximal local equivalence ratios at intake valve close appear between half of the cylinder radius and the cylinder wall, have little effect on the cylinder pressure.
Technical Paper

The Influence of Boost Pressure and Fuel Chemistry on Combustion and Performance of a HCCI Engine

2008-04-14
2008-01-0051
The influence of boost pressure (Pin) and fuel chemistry on combustion characteristics and performance of homogeneous charge compression ignition (HCCI) engine was experimentally investigated. The tests were carried out in a modified four-cylinder direct injection diesel engine. Four fuels were used during the experiments: 90-octane, 93-octane and 97-octane primary reference fuel (PRF) blend and a commercial gasoline. The boost pressure conditions were set to give 0.1, 0.15 and 0.2MPa of absolute pressure. The results indicate that, with the increase of boost pressure, the start of combustion (SOC) advances, and the cylinder pressure increases. The effects of PRF octane number on SOC are weakened as the boost pressure increased. But the difference of SOC between gasoline and PRF is enlarged with the increase of boost pressure. The successful HCCI operating range is extended to the upper and lower load as the boost pressure increased.
Journal Article

Particulate Matter Emissions from a Direct Injection Spark Ignition Engine under Cold Fast Idle Conditions for Ethanol-Gasoline Blends

2011-04-12
2011-01-1305
The engine out particular matter number (PN) distributions at engine coolant temperature (ECT) of 0° C to 40° C for ethanol/ gasoline blends (E0 to E85) have been measured for a direct-injection spark ignition engine under cold fast idle condition. For E10 to E85, PN increases modestly when the ECT is lowered. The distributions, however, are insensitive to the ethanol content of the fuel. The PN for E0 is substantially higher than the gasohol fuels at ECT below 20° C. The total PN values (obtained from integrating the PN distribution from 15 to 350 run) are approximately the same for all fuels (E0 to E85) when ECT is above 20° C. When ECT is decreased below 20° C, the total PN values for E10 to E85 increase modestly, and they are insensitive to the ethanol content. For E0, however, the total PN increases substantially. This sharp change in PN from E0 to E10 is confirmed by running the tests with E2.5 and E5. The midpoint of the transition occurs at approximately E5.
Technical Paper

Using Mass Spectrometry to Detect Ethanol and Acetaldehyde Emissions from a Direct Injection Spark Ignition Engine Operating on Ethanol/Gasoline Blends

2011-04-12
2011-01-1159
Ethanol and acetaldehyde emissions from a direct ignition spark ignition were measured using mass spectrometry. Previous methods focused on eliminating or minimizing interference from exhaust species with identical atomic mass and fragment ions created in ionization process. This paper describes a new technique which exploits the fragment ions from ethanol and acetaldehyde. A survey of mass spectra of all major species of exhaust gas was conducted. It was found that ethanol contributes most ions in mass number 31 and that no other gas species produces ions at this mass number. Acetaldehyde detection suffers more interference. Nevertheless, it was estimated that detection at mass number 43 is possible with 10% error from 2-methylbutane. This new technique was validated in an engine experiment. By running the engine with pure gasoline and E85, the validity of the technique can be checked.
Technical Paper

Spray and Combustion Characteristics of n-Butanol in a Constant Volume Combustion Chamber at Different Oxygen Concentrations

2011-04-12
2011-01-1190
A very competitive alcohol for use in diesel engines is butanol. Butanol is of particular interest as a renewable bio-fuel, as it is less hydrophilic and it possesses higher heating value, higher cetane number, lower vapor pressure, and higher miscibility than ethanol or methanol. These properties make butanol preferable to ethanol or methanol for blending with conventional diesel or gasoline fuel. In this paper, the spray and combustion characteristics of pure n-butanol fuel was experimentally investigated in a constant volume combustion chamber. The ambient temperatures were set to 1000 K, and three different oxygen concentrations were set to 21%, 16%, and 10.5%. The results indicate that the penetration length reduces with the increase of ambient oxygen concentration. The combustion pressure and heat release rate demonstrate the auto-ignition delay becomes longer with decreasing of oxygen concentrations.
Technical Paper

Effect of EGR on HCCI Combustion fuelled with Dimethyl Ether (DME) and Methanol Dual-Fuels

2005-10-24
2005-01-3730
The effects of cooled EGR on combustion and emission characteristics in HCCI operation region was investigated on a single-cylinder diesel engine, which is fitted with port injection of DME and methanol. The results indicate that EGR rate can enlarge controlled HCCI operating region, but it has little effect on the maximum load of HCCI engine fuelled with DME/methanol dual-fuels. With the increase of EGR rate, the main combustion ignition timing (MCIT) delays, the main combustion duration (MCD) prolongs, and the peak cylinder pressure and the peak rate of heat release decreases. Compared with EGR, DME percentage has an opposite effect on HCCI combustion characteristics. The increase of indicated thermal efficiency is a combined effect of EGR rate and DME percentage. Both HC and CO emissions ascend with EGR rate increasing, and decrease with DME percentage increasing. In normal combustion, NOX emissions are near zero.
Technical Paper

Simulating the Homogeneous Charge Compression Ignition Process Using a Detailed Kinetic Model for Dimethyl Ether (DME) and Methane Dual Fuel

2004-10-25
2004-01-2951
With a zero-dimensional detailed chemical kinetic model, a numerical study was carried out to investigate the chemical reaction phenomena encountered in the homogenous charge compression ignition process of dimethyl ether (DME) and methane dual fuel. The results show that the DME/methane dual fuel elementary reactions affect each other. The low temperature reaction (LTR) of DME is inhibited, the second molecular oxygen addition of DME is restrained, and β -scission plays a dominant role in DME oxidation. Hydrogen peroxide (H2O2) is controlled by DME oxidation and almost has no correlation with methane oxidation. The rich H2O2 concentration makes methane oxidation occurs at low initial temperature. Most of the formaldehyde (CH2O) is produced from H-abstraction of methoxy (CH3O) rather than from LTR of the DME. However, the heat release of methane oxidation promotes the hot flame reactions of DME which make the reactions with high activation energy occur.
Technical Paper

The Effect of PRF Fuel Octane Number on HCCI Operation

2004-10-25
2004-01-2992
By mixing iso-octane with octane number 100 and normal heptane with octane number 0, it was possible to obtain a PRF fuel with octane rating between 0 and 100. The influence of PRF fuel’s octane number on the combustion characteristics, performance and emissions character of homogeneous charge compression ignition (HCCI) engine was investigated. The experiments were carried out in a single cylinder direct injection diesel engine. The test results show that, with the increase of the octane number, the ignition timing delayed, the combustion rate decreased, and the cylinder pressure decreased. The HCCI combustion can be controlled and then extending the HCCI operating range by burning different octane number fuel at different engine mode, which engine burns low octane number fuel at low load mode and large octane number fuel at large load mode. There exists an optimum octane number that achieves the highest indicated thermal efficiency at different engine load.
Technical Paper

Experimental Study on HCCI Combustion of Dimethyl Ether(DME)/Methanol Dual Fuel

2004-10-25
2004-01-2993
Homogeneous charge compression ignition (HCCI) is considered as a high efficient and clean combustion technology for I.C. engines. Methanol is a potential fuel for HCCI combustion. In this research, a single cylinder diesel engine was applied to HCCI operation. Methanol and dimethyl ether (DME) were fueled to the engine by fuel injection system with an electric controlled port in dual fuel mode. The results show that the stable HCCI operation of DME/methanol can be obtained over a quite broad speed and load region. And compared with higher speeds, the load region is even wider at low engine speed. E.g., at the engine speed of 1000 r/min, the maximum indicated mean effective pressure(IMEP) can reach 0.77 MPa, while at 2000r/min it is 0.53 MPa. Both DME and methanol influence HCCI combustion strongly, and by regulating DME/methanol proportions the HCCI combustion process could be controlled effectively.
Technical Paper

Intake Valve Thermal Behavior During Steady-State and Transient Engine Operation

1999-10-25
1999-01-3643
Intake valve thermal behavior was observed across a wide range of operating conditions while running an engine on both propane and gasoline. Compared to the gaseous fuel, the liquid fuel operation has cooler valve temperatures (∼50-100C difference) and there is significant temperature gradient across the valve surface due to liquid fuel impinging on the front quadrant of the valve. The valve warm-up time is largely determined by the effective thermal inertia of the valve (∼valve body plus 1/3 of stem mass) and the thermal resistance to the seat. The valve is heated up by the combustion chamber; the dominant cooling paths are through the seat contact and the liquid fuel evaporation. Just after starting, very little fuel evaporates from the cold valve until there is a substantial increase in valve temperature in a period of approximately 10-20 seconds.
Technical Paper

Turbocharged diesel/CNG Dual-fuel Engines with Intercooler: Combustion, Emissions and Performance

2003-10-27
2003-01-3082
A yc6112ZLQ turbocharged 6 cylinder engine with intercooler was converted to operate in dual fuel mode with compressed natural gas (CNG) and pilot diesel. The influence of the CNG ratio, pilot diesel injection advance (ADC) and intake temperature after intercooler on the combustion process, emissions and engine performance was investigated. The results show that the combustion process of dual-fuel engines is faster than diesel engine. Both the ignition timing of the pilot fuel and the excess air ratio of total fuel λ dominate the combustion characteristics of duel-fuel engines. With the increase of CNG ratio, the pressure and temperature in cylinder decrease at rated mode, but increase at torque and low speed modes. With advanced the pilot injection timing or increased the intake temperature, the cylinder pressure and temperature increase.
Technical Paper

Experimental Study on the Effects of EGR and Octane Number of PRF Fuel on Combustion and Emission Characteristics of HCCI Engines

2005-04-11
2005-01-0174
The effects of Exhaust Gas Recirculation (EGR) and octane number of PRF fuel on combustion and emission characteristics in HCCI operation were investigated. The results show that EGR could delay the ignition timing, slow down the combustion reaction rate, reduce the pressure and average temperature in cylinder and extend the operation region into large load mode. With the increase of the fuel/air equivalence ratio or the fuel octane number (ON), the effect of EGR on combustion efficiency improves. With the increase of EGR rate, the combustion efficiency decreases. The optimum indicated thermal efficiency of different octane number fuels appears in the region of high EGR rate and large fuel/air equivalence ratio, which is next to the boundary of knocking. In the region of high EGR rate, HC emissions rise up sharply as the EGR rate increases. With the increase of octane number, this tendency becomes more obvious.
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