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Technical Paper

Large Eddy Simulation of Liquid Fuel Spray and Combustion with Gradually Varying Grid

2013-10-14
2013-01-2634
In this work, large eddy simulation (LES) with a K-equation subgrid turbulent kinetic energy model is implemented into the CFD code KIVA3V to study the features of liquid fuel spray and combustion using gradually varying grid in a constant volume chamber. The characteristic time-scale combustion model (CTC) incorporating a turbulent timescale is adopted to predict the combustion process and the SHELL auto-ignition model is used to predict auto-ignition. Combustion is also simulated using Parallel Detailed Chemistry with Lu's n-heptane reduced mechanism (58 species), which has been added into the KIVA3V-LES code. The computational results are compared with Sandia experimental data for non-reacting and reacting cases. As a result, LES can capture the complex structure of the spray and temperature distribution as well as the trend of ignition delay and flame lift-off length variations. Better results are obtained using the Parallel Detailed Chemistry than the CTC model.
Technical Paper

Influences of subgrid turbulent kinetic energy and turbulent dispersion on the characteristics of fuel spray

2011-08-30
2011-01-1839
A large eddy simulation approach and different breakup models are used to analyze fuel injection and atomization processes in a constant volume combustion bomb. The study is focused on the influences of the subgrid turbulent kinetic energy, especially the source term induced by the fuel spray, on the droplet movement and spray characteristics. Furthermore, the influence of different subgrid scale (SGS) models, including the constant coefficient and dynamic Smagorinsky models, WALE model and the K-equation turbulent energy transport model, on fuel sprays and the turbulent dispersion of droplets are examined. Factors affecting the fuel spray are discussed based on numerical computations for various operating conditions and are compared with experimental data.
Technical Paper

A Hybrid Combustion Control Strategy for Heavy Duty Diesel Engines Based on the Technologies of Multi-Pulse Injections, Variable Boost Pressure and Retarded Intake Valve Closing Timing

2011-04-12
2011-01-1382
Combustion control strategy for high efficiency and low emissions in a heavy duty (H D) diesel engine was investigated experimentally in a single cylinder test engine with a common rail fuel system, EGR (Exhaust Gas Recirculation) system, boost system and retarded intake valve closing timing actuator. For the operation loads of IMEPg (Gross Indicated Mean Effective Pressure) less than 1.1 MPa the low temperature combustion (LTC) with high rate of EGR was applied. The fuel injection modes of either single injection or multi-pulse injections, boost pressure and retarded intake valve closing timing (RIVCT) were also coupled with the engine operation condition loads for high efficiency and low emissions. A higher boost pressure played an important role in improving fuel efficiency and obtaining ultra-low soot and NOx emissions.
Technical Paper

Study on Methods of Coupling Numerical Simulation of Conjugate Heat Transfer and In-Cylinder Combustion Process in GDI Engine

2017-03-28
2017-01-0576
Wall temperature in GDI engine is influenced by both water jacket and gas heat source. In turn, wall temperature affects evaporation and mixing characteristics of impingement spray as well as combustion process and emissions. Therefore, in order to accurately simulate combustion process, accurate wall temperature is essential, which can be obtained by conjugate heat transfer (CHT) and piston heat transfer (PHT) models based on mapping combustion results. This CHT model considers temporal interaction between solid parts and cooling water. This paper presents an integrated methodology to reliably predict in-cylinder combustion process and temperature field of a 2.0L GDI engine which includes engine head/block/gasket and water jacket components. A two-way coupling numerical procedure on the basis of this integrated methodology is as follows.
Technical Paper

Combustion Characteristics of Acetone, Butanol, and Ethanol (ABE) Blended with Diesel in a Compression-Ignition Engine

2016-04-05
2016-01-0884
Acetone-Butanol-Ethanol (ABE) is an intermediate product in the ABE fermentation process for producing bio-butanol. As an additive for diesel, it has been shown to improve spray evaporation, improve fuel atomization, enhance air-fuel mixing, and enhance combustion as a whole. The typical compositions of ABE are in a volumetric ratio of 3:6:1 or 6:3:1. From previous studies done in a constant volume chamber, it was observed that the presence of additional acetone in the blend caused advancement in the combustion phasing, but too much acetone content led to an increase in soot emission during combustion. The objective of this research was to investigate the combustion of these mixtures in a diesel engine. The experiments were conducted in an AVL 5402 single-cylinder diesel engine at different speeds and different loads to study component effects on the various engine conditions. The fuels tested in these experiments were D100, ABE(3:6:1)10, ABE(3:6:1)20, ABE(6:3:1)10, and ABE(6:3:1)20.
Technical Paper

Experimental Study on Impingement of Fuel Droplet on Substrates

2019-04-02
2019-01-0300
Within a gasoline direct injection (GDI) engine, the impingement of fuel droplet on substrates induces various problems such as particular matter emission, oil dilution and abnormal combustion. Therefore, in order to solve these problems, it is urgent to have a clear understanding of the impingement behavior of fuel droplet impacting on substrates. Most previous studies have focused on the impingement of either water droplet on dry solid surface or the impinging droplet on the liquid film of the same type of liquid, while little research has been conducted on the impingement of fuel droplet on relevant substrates existing in GDI engines. The impingement of fuel droplet with higher Weber number on dry surface, fuel film and oil film with different thickness and viscosity were investigated experimentally. Results show that fuel droplet impacting on dry wall is easy to be deposited to form a fuel film. The fuel film attached to the wall is the main reason for the splash.
Technical Paper

Characteristics of Single Fuel Droplet Impact on Oil Film

2019-04-02
2019-01-0304
In order to better understand the spray impingement behavior of the gasoline direct injection (GDI) engine, this paper used the laser induced fluorescence (LIF) test method to conduct basic research on the fuel droplet impact onto the oil film. The effects of different incident droplet Weber number, dimensionless oil film thickness and oil film viscosity on the morphology of oil film after impact were investigated. And the composition of splashing droplets after impingement was analyzed. The morphology of oil film after impact was divided into three categories: stable crown, delayed splash crown, and prompt splash crown. The stable crown has only splashing fuel droplets, the splashing droplets of delayed splash crown are consist of fuel and oil film. The splashing droplets of prompt splash crown mainly include the oil film. It is shown that the larger the Weber number of incident droplets, the larger the dimensionless crown height and diameter, the easier the oil film will splash.
Technical Paper

Experimental Study on Combustion Characteristics of Methane/Gasoline Dual-Fuel in a SI Engine at Different Load Conditions

2018-04-03
2018-01-1140
Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions.
Technical Paper

Effect of Turbulence-Chemistry Interaction on Spray Combustion: A Large Eddy Simulation Study

2019-04-02
2019-01-0203
Although turbulence plays a critical role in engines operated within low temperature combustion (LTC) regime, its interaction with chemistry on auto-ignition at low-ambient-temperature and lean-oxygen conditions remains inadequately understood. Therefore, it is worthwhile taking turbulence-chemistry interaction (TCI) into consideration in LTC engine simulation by employing advanced combustion models. In the present study, large eddy simulation (LES) coupled with linear eddy model (LEM) is performed to simulate the ignition process in n-heptane spray under engine-relevant conditions, known as Spray H. With LES, more details about unsteady spray flame could be captured compared to Reynolds-averaged Navier-Stokes equations (RANS). With LEM approach, both scalar fluctuation and turbulent mixing on sub-grid level are captured, accounting for the TCI. A skeletal mechanism is adopted in this numerical simulation, including 41 species and 124 reactions.
Technical Paper

An Experimental Study of the Combustion, Performance and Emission Characteristics of a CI Engine under Diesel-1-Butanol/CNG Dual Fuel Operation Mode

2016-04-05
2016-01-0788
In order to comply with the stringent emission regulations, many researchers have been focusing on diesel-compressed natural gas (CNG) dual fuel operation in compression ignition (CI) engines. The diesel-CNG dual fuel operation mode has the potential to reduce both the soot and NOx emissions; however, the thermal efficiency is generally lower than that of the pure diesel operation, especially under the low and medium load conditions. The current experimental work investigates the potential of using diesel-1-butanol blends as the pilot fuel to improve the engine performance and emissions. Fuel blends of B0 (pure diesel), B10 (90% diesel and 10% 1-butanol by volume) and B20 (80% diesel and 20% 1-butanol) with 70% CNG substitution were compared based on an equivalent input energy at an engine speed of 1200 RPM. The results indicated that the diesel-1-butanol pilot fuel can lead to a more homogeneous mixture due to the longer ignition delay.
Technical Paper

Selection of Swirl Ratio in Diesel Engines Based on Droplet Trajectory Analysis

2017-03-28
2017-01-0813
Matching fuel injection and airflow motion is critical for the optimization of fuel-air mixing and combustion process in diesel engines. In this study, the effects of swirl flow on liquid droplet motion and the selection of swirl ratio, which are known as the major concern in organizing airflow motion, were investigated based on theoretical analysis of droplet trajectories. The evaporating droplets with various initial conditions are assumed to be transported in a solid-body-like swirl field, and their trajectories were derived based on force analysis. To evaluate fuel-air mixing quality, a new parameter with respect to fuel vapor distribution was proposed. Based on this methodology, the effects of swirl velocity, droplet size, as well as liquid-gas density ratio on droplet trajectory were discussed under diesel-engine-like boundary conditions.
Technical Paper

Experimental Comparison between Stratified Flame Ignition and Micro Flame Ignition in a Gasoline SI-CAI Hybrid Combustion Engine

2017-03-28
2017-01-0737
Controlled Auto-Ignition (CAI), also known as Homogeneous charge compression ignition (HCCI), has been the subject of extensive research because of their ability to providing simultaneous reduction in fuel consumption and NOx emissions in a gasoline engine. However, due to its limited operation range, combustion mode switching between CAI and spark ignition (SI) combustion is essential to cover the overall operational range of a gasoline engine for passenger car applications. Previous research has shown that the SI-CAI hybrid combustion has the potential to control the ignition timing and heat release process during both steady state and transient operations. However, it was found that the SI-CAI hybrid combustion process is often characterized with large cycle-to-cycle variations, due to the flame instability at high dilution conditions.
Technical Paper

Numerical Study on a High Efficiency Gasoline Reformed Molecule HCCI Combustion Using Exergy Analysis

2017-03-28
2017-01-0735
In this study, the characteristics and the advantages on engine performance of the reformed molecule HCCI (RM-HCCI) combustion fueled with gasoline were investigated by exergy analysis. The processes of fuel reforming and the closed portion of the engine cycle were simulated integrated with chemical kinetics mechanism at varied compression ratio (CR) and constant speed conditions. Results showed the fuel reforming under high temperature and oxygen-free condition by the exhaust heat recovery and electric heating assistance could drive gasoline to transform to the small-molecule gas fuels, meanwhile enhanced the chemical exergy of the fuel. The reformed fuel contributed to extending ignition delay, so less dilution required in RM-HCCI engine when expanding high load compared with gasoline HCCI engine. Thus, RM-HCCI engine could achieve higher load than gasoline HCCI engine, with the improvements by 12%, 26%, and 31% at CR17, CR19, and CR21, respectively.
Technical Paper

Comparing the Exergy Destruction of Methanol and Gasoline in Reactivity Controlled Compression Ignition (RCCI) Engine

2017-03-28
2017-01-0758
Multi-dimensional models coupled with a reduced chemical mechanism were used to investigate the effect of fuel on exergy destruction fraction and sources in a reactivity controlled compression ignition (RCCI) engine. The exergy destruction due to chemical reaction (Deschem) makes the largest contribution to the total exergy destruction. Different from the obvious low temperature heat release (LTHR) behavior in gasoline/diesel RCCI, methanol has a negative effect on the LTHR of diesel, so the exergy destruction accumulation from LTHR to high temperature heat release (HTHR) can be avoided in methanol/diesel RCCI, contributing to the reduction of Deschem. Moreover, the combustion temperature in methanol/diesel RCCI is higher compared to gasoline/diesel RCCI, which is also beneficial to the lower exergy destruction fraction. Therefore, the exergy destruction of methanol/diesel RCCI is lower than that of gasoline/diesel RCCI at the same combustion phasing.
Technical Paper

The Evaporation Characteristics of Cylinder Oil of Low-Speed 2-Stroke Marine Engines

2017-03-28
2017-01-0886
The combustion of cylinder lubricating oil (called as cylinder oil for short) is one of the major sources of PM emissions of low-speed 2-stroke marine diesel engines. For pre-mixed combustion low-speed 2-stroke marine gas engines, the auto-ignition of cylinder oil might result in knock or more hazard abnormal combustion - pre-ignition. Evaporation is a key sub-process of the auto-ignition process of cylinder oil droplets. The evaporation behavior has a profound impact on the auto-ignition and combustion processes of cylinder oil droplets, and a great influence on engine combustion performance and emission characteristics. This paper applied an oil suspending apparatus to investigate the evaporation behavior of cylinder oil droplets and base oil droplets. The effects of ambient temperatures on the evaporation process were measured and analyzed. The results indicate that the evaporation of cylinder oil includes heating, evaporating, pyrolysis, and polymerization.
Technical Paper

Effect of Acetone-Gasoline Blend Ratio on Combustion and Emissions Characteristics in a Spark-Ignition Engine

2017-03-28
2017-01-0870
Due to the increasing consumption of fossil fuels, alternative fuels in internal combustion engines have attracted a lot of attention in recent years. Ethanol is the most common alternative fuel used in spark ignition (SI) engines due to its advantages of biodegradability, positively impacting emissions reduction as well as octane number improvement. Meanwhile, acetone is well-known as one of the industrial waste solvents for synthetic fibers and most plastic materials. In comparison to ethanol, acetone has a number of more desirable properties for being a viable alternative fuel such as its higher energy density, heating value and volatility.
Technical Paper

A Theoretical Investigation of the Combustion of PRF90 under the Flexible Cylinder Engine Mode

2017-03-28
2017-01-1027
On-board fuel reforming offers a prospective clean combustion mode for the engines. The flexible cylinder engine strategy (FCE) is a new kind of such mode. In this paper, the combustion of the primary reference fuel of PRF90 was theoretically investigated in a homogeneous charge compression ignition engine to validate the FCE mode, mainly focusing on the ignition delay time, the flame speed, and the emissions. The simulations were performed by using the CHEMKIN2.0 package to demonstrate the fuel reforming process in the flexible cylinder, the cooling effect on the reformed products, and the combustions of the mixture of the fresh fuel and the reformed products in the normal cylinders. It was found that the FCE mode decreased the ignition delay time of the fuel by about 35 crank angles at a typical engine condition.
Technical Paper

Control-Oriented Modeling of Soot Emissions in Gasoline Partially Premixed Combustion with Pilot Injection

2017-03-28
2017-01-0511
In this paper, a control-oriented soot model was developed for real-time soot prediction and combustion condition optimization in a gasoline Partially Premixed Combustion (PPC) Engine. PPC is a promising combustion concept that achieves high efficiency, low soot and NOx emissions simultaneously. However, soot emissions were found to be significantly increased with high EGR and pilot injection, therefore a predictive soot model is needed for PPC engine control. The sensitivity of soot emissions to injection events and late-cycle heat release was investigated on a multi-cylinder heavy duty gasoline PPC engine, which indicated main impact factors during soot formation and oxidation processes. The Hiroyasu empirical model was modified according to the sensitivity results, which indicated main influences during soot formation and oxidation processes. By introducing additional compensation factors, this model can be used to predict soot emissions under pilot injection.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of Stoichiometric Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

2019-04-02
2019-01-0960
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion.
Technical Paper

Dilution Boundary Expansion Mechanism of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

2019-04-02
2019-01-0954
In decade years, Spark Ignition-Controlled Auto Ignition (SI-CAI) hybrid combustion, also called Spark Assisted Compression Ignition (SACI) has shown its high-efficiency and low emissions advantages. However, high dilution causes the problem of unstable initial ignition and flame propagation, which leads to high cyclic variation of heat release and IMEP. The instability of SI-CAI hybrid combustion limits its dilution degree and its ability to improve the thermal efficiency. In order to solve instability problems and expand the dilution boundary of hybrid combustion, micro flame ignition (MFI) strategy is applied in gasoline hybrid combustion engines. Small amount of Dimethyl Ether (DME) chosen as the ignition fuel is injected into cylinder to form micro flame kernel, which can stabilize the ignition combustion process.
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