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Technical Paper

Numerical Investigation of the Combustion Kinetics of Partially Premixed Combustion (PPC) Fueled with Primary Reference Fuel

2020-04-14
2020-01-0554
This work numerically investigates the detailed combustion kinetics in a gasoline compression ignition (GCI) engine using three fuel injection strategies, including single-injection, double-injection, port fuel injection and direct injection (PFI+DI). A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict GCI combustion under various operating conditions. To provide insight into key reaction pathways, a post-process tool was used. The validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how the ignition occurs during the low-to high-temperature reaction transition and how it varies due to single- and double-injection and PFI+DI injection strategies.
Technical Paper

Modelling of a Discrete Variable Compression Ratio (VCR) System for Fuel Consumption Evaluation - Part 2: Modelling Results

2019-04-02
2019-01-0472
Variable Compression Ratio systems are an increasingly attractive solution for car manufacturers in order to reduce vehicle fuel consumption. By having the capability to operate with a range of compression ratios, engine efficiency can be significantly increased by operating with a high compression ratio at low loads, where the engine is normally not knock-limited, and with a low compression ratio at high load, where the engine is more prone to knock. In this way, engine efficiency can be maximized without sacrificing performance. This study aims to analyze how the effectiveness of a VCR system is affected by various powertrain and vehicle parameters. By using a Matlab model of a VCR system developed in Part 1 of this work, the influence of the vehicle characteristics, the drive cycle, and of the number of stages used in the VCR system was studied.
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

Natural Flame Luminosity and Emission Spectra of Diesel Spray Flame under Oxygen-Enriched Condition in an Optical Constant Volume Vessel

2018-09-10
2018-01-1781
The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity.
Technical Paper

Design and Validation of a GT Power Model of the CFR Engine towards the Development of a Boosted Octane Number

2018-04-03
2018-01-0214
Developments in modern spark ignition (SI) engines such as intake boosting, direct-injection, and engine downsizing techniques have demonstrated improved performance and thermal efficiency, however, these strategies induce significant deviation in end-gas pressure/temperature histories from those of the traditional Research and Motor Octane Number (RON and MON) standards. Attempting to extrapolate the anti-knock performance of fuels tested under the traditional RON/MON conditions to boosted operation has yielded mixed results in both SI and advanced compression ignition (ACI) engines. This consideration motivates the present work with seeks to establish a pathway towards the development of the test conditions of a boosted octane number, which would better correlate to fuel performance at high intake pressure conditions.
Journal Article

The Development of an Ignition Delay Correlation for PRF Fuel Blends from PRF0 (n-Heptane) to PRF100 (iso-Octane)

2016-04-05
2016-01-0551
A correlation was developed to predict the ignition delay of PRF blends at a wide range of engine-relevant operating conditions. Constant volume simulations were performed using Cantera coupled with a reduced reaction mechanism at a range of initial temperatures from 570-1860K, initial pressures from 10-100atm, oxygen mole percent from 12.6% to 21%, equivalence ratios from 0.30-1.5, and PRF blends from PRF0 to PRF100. In total, 6,480 independent ignition delay simulations were performed. The correlation utilizes the traditional Arrhenius formulation; with equivalence ratio (φ), pressure (p), and oxygen mole percentage (xo2) dependencies. The exponents α, β, and γ were fitted to a third order polynomial with respect to temperature with an exponential roll-off to a constant value at low temperatures to capture the behavior expressed by the reaction mechanism. The location and rate of the roll-off functions were modified by linear functions of PRF.
Technical Paper

Numerical Study of the RCCI Combustion Processes Fuelled with Methanol, Ethanol, n-Butanol and Diesel

2016-04-05
2016-01-0777
In the current, numerical study RCCI combustion and emission characteristics using various fuel strategies are investigated, including methanol, ethanol, n-butanol and gasoline as the low reactivity fuel, and diesel fuel as the high reactivity fuel. A reduced Primary Reference Fuel (PRF)-alcohol chemical kinetic mechanism was coupled with a computational fluid dynamic (CFD) code to predict RCCI combustion under various operating conditions. The results show that a higher quantity of diesel was required to maintain the same combustion phasing with alcohol-diesel fuel blends, and the combustion durations and pressure rise rates of methanol-diesel (MD) and ethanol-diesel (ED) cases were much shorter and higher than those of gasoline-diesel (GD) and n-butanol-diesel (nBD) cases. The simulations also investigated the sensitivities of the direct injection strategies, intake temperature and premixed fuel ratio on RCCI combustion phasing control.
Journal Article

Numerical Study of RCCI and HCCI Combustion Processes Using Gasoline, Diesel, iso-Butanol and DTBP Cetane Improver

2015-04-14
2015-01-0850
Reactivity Controlled Compression Ignition (RCCI) has been shown to be an attractive concept to achieve clean and high efficiency combustion. RCCI can be realized by applying two fuels with different reactivities, e.g., diesel and gasoline. This motivates the idea of using a single low reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver to achieve RCCI combustion. In the current study, numerical investigation was conducted to simulate RCCI and HCCI combustion and emissions with various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol+di-tert-butyl peroxide (DTBP) cetane improver. A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP mechanism was formulated and coupled with the KIVA computational fluid dynamic (CFD) code to predict the combustion and emissions of these fuels under different operating conditions in a heavy duty diesel engine.
Journal Article

Improving the Understanding of Intake and Charge Effects for Increasing RCCI Engine Efficiency

2014-04-01
2014-01-1325
The present experimental engine efficiency study explores the effects of intake pressure and temperature, and premixed and global equivalence ratios on gross thermal efficiency (GTE) using the reactivity controlled compression ignition (RCCI) combustion strategy. Experiments were conducted in a heavy-duty single-cylinder engine at constant net load (IMEPn) of 8.45 bar, 1300 rev/min engine speed, with 0% EGR, and a 50% mass fraction burned combustion phasing (CA50) of 0.5°CA ATDC. The engine was port fueled with E85 for the low reactivity fuel and direct injected with 3.5% 2-ethylhexyl nitrate (EHN) doped into 91 anti-knock index (AKI) gasoline for the high-reactivity fuel. The resulting reactivity of the enhanced fuel corresponds to an AKI of approximately 56 and a cetane number of approximately 28. The engine was operated with a wide range of intake pressures and temperatures, and the ratio of low- to high-reactivity fuel was adjusted to maintain a fixed speed-phasing-load condition.
Technical Paper

RCCI Engine Operation Towards 60% Thermal Efficiency

2013-04-08
2013-01-0279
The present experimental study explored methods to obtain the maximum practical cycle efficiency with Reactivity Controlled Compression Ignition (RCCI). The study used both zero-dimensional computational cycle simulations and engine experiments. The experiments were conducted using a single-cylinder heavy-duty research diesel engine adapted for dual fuel operation, with and without piston oil gallery cooling. In previous studies, RCCI combustion with in-cylinder fuel blending using port-fuel-injection of a low reactivity fuel and optimized direct-injections of higher reactivity fuels was demonstrated to permit near-zero levels of NOx and PM emissions in-cylinder, while simultaneously realizing gross indicated thermal efficiencies in excess of 56%. The present study considered RCCI operation at a fixed load condition of 6.5 bar IMEP an engine speed of 1,300 [r/min]. The experiments used a piston with a flat profile with 18.7:1 compression ratio.
Technical Paper

Experimental and Modeling Study of Biodiesel Surrogates Combustion in a CI Engine

2013-04-08
2013-01-1130
This work concerns the oxidation of biodiesel surrogates in a CI engine. An experimental study has been carried out in a single-cylinder common-rail CI engine with soybean biodiesel and two biodiesel surrogates containing neat methyl decanoate and methyl decanoate/n-heptane blends. Tests have been conducted with various intake oxygen concentrations ranging from 21% to approximately 9% at intake temperatures of 25°C and 50°C. The results showed that the ignition delay and smoke emissions of neat methyl decanoate were closer to that of soybean biodiesel as compared with methyl decanoate/n-heptane blends. A reduced chemical kinetic mechanism for the oxidation of methyl decanoate has been developed and applied to model internal combustion engines. A KIVA code, coupled with the Chemkin chemistry solver, was used as the computational platforms. The effects of various intake oxygen concentrations on the in-cylinder emissions of OH and soot were discussed.
Technical Paper

Comparison of Diesel Combustion CFD Models and Evaluation of the Effects of Model Constants

2012-04-16
2012-01-0134
This paper describes numerical simulations that compare the performance of two combustion CFD models against experimental data, and evaluates the effects of combustion and spray model constants on the predicted combustion and emissions under various operating conditions. The combustion models include a Characteristic Time Combustion (CTC) model and CHEMKIN with reduced chemistry models integrated in the KIVA-3Vr2 CFD code. The diesel spray process was modeled using an updated version of the KH-RT spray model that features a gas jet submodel to help reduce numerical grid dependencies, and the effects of both the spray and combustion model constants on combustion and emissions were evaluated. In addition, the performance of two soot models was compared, namely a two-step soot model, and a more detailed model that considers soot formation from PAH precursors.
Technical Paper

Study of Biodiesel Combustion in a Constant Volume Chamber with Different Ambient Temperature and Oxygen Concentration

2011-08-30
2011-01-1931
Biodiesel is a widely used biofuel in diesel engines, which is of particular interest as a renewable fuel because it possesses the similar properties as the diesel fuel. The pure soybean biodiesel was tested in an optical constant volume combustion chamber using natural flame luminosity and forward illumination light extinction (FILE) methods to explore the combustion process and soot distribution at various ambient temperatures (800 K and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results indicated that, with a lower ambient temperature, the autoignition delay became longer for all three oxygen concentrations and more ambient air was entrained by spray jet and more fuel was burnt by premixed combustion. With less ambient oxygen concentration, the heat release rate showed not only a longer ignition delay but also longer combustion duration.
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.
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