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Technical Paper

A CFD Investigation into the Effects of Intake Valves Events on Airflow Characteristics in a Motored 4-Valve Engine Cylinder with Negative Valve Overlapping

2007-09-16
2007-24-0032
This paper presents a computational study of the airflow features within a motored 4-valve direct injection engine cylinder. An unconventional intake valve strategy was investigated; whereby each valve on the pair of intake valves was assumed to be actuated with different lifts and duration. One of the intake valves was assumed to follow a high-lift long duration valve-lift profile while the other was assumed to follow a low-lift short duration valve-lift profile. The pair of exhaust valves was assumed to be actuated with two identical low-lift short duration valve-lift profiles in order to generate the so-called negative valve overlapping (NVO). The in-cylinder flow fields developed with such intake valve strategy were compared to those produced in the same engine cylinder but with the application of identical low-lift short duration intake valve events.
Technical Paper

Residual Gas Trapping for Natural Gas HCCI

2004-06-08
2004-01-1973
With the high auto ignition temperature of natural gas, various approaches such as high compression ratios and/or intake charge heating are required for auto ignition. Another approach utilizes the trapping of internal residual gas (as used before in gasoline controlled auto ignition engines), to lower the thermal requirements for the auto ignition process in natural gas. In the present work, the achievable engine load range is controlled by the degree of internal trapping of exhaust gas supplemented by intake charge heating. Special valve strategies were used to control the internal retention of exhaust gas. Significant differences in the degree of valve overlap were necessary when compared to gasoline operation at the same speeds and loads, resulting in lower amounts of residual gas observed. The dilution effect of residual gas trapping is hence reduced, resulting in higher NOx emissions for the stoichiometric air/fuel ratio operation as compared to gasoline.
Technical Paper

Effect of Hydrogen Addition on Natural Gas HCCI Combustion

2004-06-08
2004-01-1972
Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve HCCI (homogeneous charge compression ignition) engine operation. Previous work by the authors has shown that hydrogen addition improves combustion stability in various difficult combustion conditions. It is shown here that hydrogen, together with residual gas trapping, helps also in lowering the intake temperature required for HCCI. It has been argued in literature that the addition of hydrogen advances the start of combustion in the cylinder. This would translate into the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke. The experimental results of this work show that, with hydrogen replacing part of the fuel, a decrease in intake air temperature requirement is observed for a range of engine loads, with larger reductions in temperature noted at lower loads.
Technical Paper

CFD Analysis of Air Intake System with Negative Pressure on Intake Grill

2008-06-23
2008-01-1643
The objective of the current research was to predict and analyze the flow through the grill of air intake system which is positioned behind the front wheel arch of vehicle. Most of the vehicle used today locates the grill of air intake at the front side so to acquire benefit of ram effect. In some cases, however, the grill is located behind the vehicle to improve wading performance. The geometry of air intake system of Land Rover Freelander was used in the modelling approach. The study was focused on different flow speeds on the grill at high load operation where the air speed at the grill side is high and creates negative pressure. The CFD results are validated against experimental data of steady flow test bench.
Technical Paper

Effect of Intake Valves Timings on In-Cylinder Charge Characteristics in a DI Engine Cylinder with Negative Valve Overlapping

2008-04-14
2008-01-1347
This paper presents a computational investigation of the in-cylinder charge characteristics within a motored 4-valve direct injection HCCI engine cylinder with applied negative valve overlapping. Non-typical intake valve strategy was investigated; whereby the pair of intake valves was assumed to follow the same low-lift short-duration valve-lift profile but actuated at different timings. The phase of intake-valve-opening relative to that of exhaust-valve-closing was optimized in terms of pumping losses. The flow fields generated with such an intake valve strategy were compared to those produced in the same engine cylinder but with typical early and late intake-valve-timing. The computational results of such an approach showed modifications in the in-cylinder swirl and tumble motions during the intake and compression strokes.
Technical Paper

A 1D Analysis into the Effect of Variable Valve Timing on HCCI Engine Parameters

2008-10-06
2008-01-2459
The effects of variable intake-valve-timing on the gas exchange process and performance of a 4-valve direct-injection HCCI engine were computationally investigated using a 1D gas dynamics engine cycle simulation code. A non-typical strategy to actuate the pair of intake valves was examined; whereby each valve was assumed to be actuated independently at different timing. Using such an intake valves strategy, the obtained results showed a considerable improvement of the engine parameters such as load and charging efficiency as compared with the typical identical intake valve pair timings case. Additional benefits of minimizing pumping losses and improving the fuel economy were demonstrated with the use of the non-simultaneous actuation of the intake valve pair having the opening timing of the early intake valve coupled with a symmetric degree of crank angle for the timing of exhaust valve closing.
Technical Paper

Modelling Study of Combustion and Gas Exchange in a HCCI (CAI) Engine

2002-03-04
2002-01-0114
The main obstacle for the development of Homogeneous Charge Compression Ignition (HCCI) engines is the control of auto-ignition timing, and one key is to control the trapped gas temperature so as to enable the autoignition at the end of compression stroke. Using special valve mechanisms, very high residual gas mass fraction can be achieved to raise the charge temperature. Gas exchange process hence plays a crucial role in such HCCI engines because of its strong interaction with combustion. The modification of the gas exchange process in a 4-stroke automotive engine for HCCI combustion is not straightforward, since the engine must be able to operate across a considerably wide range of speeds and loads. Intake air temperatures and the valve mechanism need to be controlled in order to deliver optimal engine performance and fuel economy. This paper presents a modelling study of the combustion and gas exchange in a HCCI engine.
Technical Paper

Effect of inlet valve timing on boosted gasoline HCCI with residual gas trapping

2005-05-11
2005-01-2136
With boosted HCCI operation on gasoline using residual gas trapping, the amount of residuals was found to be of importance in determining the boundaries of stable combustion at various boost pressures. This paper represents a development of this approach by concentrating on the effects of inlet valve events on the parameters of boosted HCCI combustion with residual gas trapping. It was found that an optimum inlet valve timing could be found in order to minimize NOx emissions. When the valve timing is significantly advanced or retarded away from this optimum, NOx emissions increase due to the richer air / fuel ratios required for stable combustion. These richer conditions are necessary as a result of either the trapped residual gases becoming cooled in early backflow or because of lowering of the effective compression ratio. The paper also examines the feasibility of using inlet valve timing as a method of controlling the combustion phasing for boosted HCCI with residual gas trapping.
Technical Paper

In-cylinder Flow with Negative Valve Overlapping - Characterised by PIV Measurement

2005-05-11
2005-01-2131
Negative valve overlapping is widely used for trapping residual burned gas within the cylinder to enable controlled Homogeneous Charge Compression Ignition (HCCI). HCCI has been shown as a promising combustion technology to improve the fuel economy and NOx emissions of gasoline engines. While the importance of in-cylinder flow in the fuel and air mixing process is recognised, the characteristics of air motion with specially designed valve events having reduced valve lift and durations associated with HCCI engines and their effect on subsequent combustion are not yet fully understood. This paper presents an investigation in an optical engine designed for HCCI combustion using EGR trapping. PIV techniques have been used to measure the in-cylinder flow field under motored conditions and a quantitative analysis has been carried out for the flow characterisation with comparison made against the flow in the same engine with conventional valve strategies for SI combustion.
Technical Paper

An Experimental Study of Combustion Initiation and development in an Optical HCCI Engine

2005-05-11
2005-01-2129
The major characteristics of the combustion in Homogeneous Charge Compression Ignition (HCCI) engines, irrespective of the technological strategy used to enable the ‘controlled auto-ignition’, are that the mixture of fuel and air is preferably premixed and largely homogeneous. Ignition tends to take place simultaneously at multiple points and there is no bulk flame propagation as in conventional spark-ignition (SI) engines. This paper presents an experimental study of flame development in an optical engine operating in HCCI combustion mode. High resolution and high-speed charge coupled device (CCD) cameras were used to take images of the flame during the combustion process. Fuels include gasoline, natural gas (NG) and hydrogen addition to NG all at stoichiometric conditions, permitting the investigation of combustion development for each fuel. The flame imaging data was supplemented by simultaneously recorded in-cylinder pressure data.
Technical Paper

Study on an Electronically Controlled Common-Rail Injection System for Liquefied Alternative Fuels

2005-05-11
2005-01-2085
Liquefied alternative fuels offer great potential benefits in reducing exhaust emissions and improving fuel economy of automotive engines. In order to achieve the best performance of the engine running with such fuels, it is critical to have an appropriate fuel system. In the present work, a new electronically controlled common-rail injection system has been specially designed and tested for the direct injection of liquefied alternative fuels, since a conventional pump-line-injector injection system in the conventional diesel engine was not suitable for the purpose. Experimental work has been carried out to examine and improve matching of the fuel injection system on a new fuel injection pump test bench. The preliminary engine bench test has demonstrated that this arrangement meets the requirement for the operating characteristics of a fuel injection system in a direct injection diesel engine operating with dimethyl ether (DME).
Technical Paper

Phenomenology of EGR in a Light Duty Diesel Engine Fuelled with Hydrogenated Vegetable Oil (HVO), Used Vegetable Oil Methyl Ester (UVOME) and Their Blends

2013-04-08
2013-01-1688
HVO contains paraffin only and UVOME is methyl ester with long chain alkyl while mineral diesel is complex compound and contains lots of aromatic and Naphthenic. This paper compares the effects of EGR on the two different types of biodiesels blends compared to diesel. The combustion performance and emissions of biodiesel blends of UVOME and HVO were investigated in a turbocharged direct injection V6 diesel engine with EGR swept from 0% to the calibration setting for diesel. The EGR sweep tests with increment of 5% were conducted at the engine speed of 1500 RPM for the load of between 72 Nm to 143 Nm, using sulfur-free diesel blended with UVOME and HVO at 30% and 60% by volume respectively. As the EGR rate was increased, the brake specific fuel consumption (BSFC) for each fuel was reduced at lower load but increased at higher load. The BSFC of mineral diesel was lower than UVOME blends and similar to the HVO blends.
Technical Paper

Numerical Study of DMF and Gasoline Spray and Mixture Preparation in a GDI Engine

2013-04-08
2013-01-1592
2, 5-Dimethylfuran (DMF) has been receiving increasing interest as a potential alternative fuel to fossil fuels, owing to the recent development of new production technology. However, the influence of DMF properties on the in-cylinder fuel spray and its evaporation, subsequent combustion processes as well as emission formation in current gasoline direct injection (GDI) engines is still not well understood, due to the lack of comprehensive understanding of its physical and chemical characteristics. To better understand the spray characteristics of DMF and its application to the IC engine, the fuel sprays of DMF and gasoline were investigated by experimental and computational methods. The shadowgraph and Phase Doppler Particle Analyzer (PDPA) techniques were used for measuring spray penetration, droplet velocity and size distribution of both fuels.
Technical Paper

Study of Near Nozzle Spray Characteristics of Ethanol under Different Saturation Ratios

2016-10-17
2016-01-2189
Atomization of fuel sprays is a key factor in controlling the combustion quality in the direct-injection engines. In this present work, the effect of saturation ratio (Rs) on the near nozzle spray patterns of ethanol was investigated using an ultra-high speed imaging technique. The Rs range covered both flash-boiling and non-flash boiling regions. Ethanol was injected from a single-hole injector into an optically accessible constant volume chamber at a fixed injection pressure of 40 MPa with different fuel temperatures and back pressures. High-speed imaging was performed using an ultrahigh speed camera (1 million fps) coupled with a long-distance microscope. Under non-flash boiling conditions, the effect of Rs on fuel development was small but observable. Clear fuel collision can be observed at Rs=1.5 and 1.0. Under the flash boiling conditions, near-nozzle spray patterns were significant different from the non-flash boiling ones.
Journal Article

Spray Characteristics Study of DMF Using Phase Doppler Particle Analyzer

2010-05-05
2010-01-1505
2,5-dimethylfuran (DMF) is currently regarded as a potential alternative fuel to gasoline due to the development of new production technology. In this paper, the spray characteristics of DMF and its blends with gasoline were studied from a high pressure direct injection gasoline injector using the shadowgraph and Phase Doppler Particle Analyzer (PDPA) techniques, This includes the spray penetration, droplet velocity and size distribution of the various mixtures. In parallel commercial gasoline and ethanol were measured in order to compare the characteristics of DMF. A total of 52 points were measured along the spray so that the experimental results could be used for subsequent numerical modeling. In summary, the experimental results showed that DMF and its blends have similar spray properties to gasoline, compared to ethanol. The droplet size of DMF is generally smaller than ethanol and decreases faster with the increase of injection pressure.
Journal Article

The Particle Emissions Characteristics of a Light Duty Diesel Engine with 10% Alternative Fuel Blends

2010-05-05
2010-01-1556
In this study, the particle emission characteristics of 10% alternative diesel fuel blends (Rapeseed Methyl Ester and Gas-to-Liquid) were investigated through the tests carried out on a light duty common-rail Euro 4 diesel engine. Under steady engine conditions, the study focused on particle number concentration and size distribution, to comply with the particle metrics of the European Emission Regulations (Regulation NO 715/2007, amended by 692/2008 and 595/2009). The non-volatile particle characteristics during the engine warming up were also investigated. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, can result in a noticeable reduction of the total particle numbers; however, the number of nucleation mode particles can increase in certain cases.
Technical Paper

Numerical Investigation of GDI Injector Nozzle Geometry on Spray Characteristics

2015-09-01
2015-01-1906
The large eddy simulation (LES) with Volume of Fluid (VOF) interface tracking method in Ansys-FLUENT has been used to study the effects of nozzle hole geometrical parameters on gasoline direct injection (GDI) fuel injectors, namely the effect of inner hole length/diameter (L/D) ratio and counter-bore diameters on near field spray characteristics. Using iso-octane as a model fuel at the fuel injection pressure of 200 bar, the results showed that the L/D ratio variation of the inner hole has a more significant influence on the spray characteristics than the counter-bore diameter variation. Reducing the L/D ratio effectively increases the mass flow rate, velocity, spray angle and reduces the droplet size and breakup length. The increased spray angle results in wall impingements inside the counter-bore cavity, particularly for L/D=1 which can potentially lead to increased deposit accumulation inside fuel injectors.
Journal Article

Transient Emissions Characteristics of a Turbocharged Engine Fuelled by Biodiesel Blends

2013-04-08
2013-01-1302
The effects of different biodiesel blends on engine-out emissions under various transient conditions were investigated in this study using fast response diagnostic equipment. The experimental work was conducted on a modern 3.0 L, V6 high pressure common rail diesel engine fuelled with mineral diesel (B0) and three different blends of rapeseed methyl esters (RME) (B30, B60, B100 by volume) without any modifications of engine parameters. DMS500, Fast FID and Fast CLD were used to measure particulate matter (PM), total hydrocarbon (THC) and nitrogen monoxide (NO) respectively. The tests were conducted during a 12 seconds period with two tests in which load and speed were changed simultaneously and one test with only load changing. The results show that as biodiesel blend ratio increased, total particle number (PN) and THC were decreased whereas NO was increased for all the three transient conditions.
Technical Paper

Improving Ethanol-Diesel Blend Through the Use of Hydroxylated Biodiesel

2014-10-13
2014-01-2776
Due to the emission benefits of the oxygen in the fuel molecule, the interest for the use of ethanol as fuel blend components in compression ignition engines has been increased. However the use of fuel blends with high percentage of ethanol can lead to poor fuel blend quality (e.g. fuel miscibility, cetane number, viscosity and lubricity). An approach which can be used to improve these properties is the addition of biodiesel forming ternary blends (ethanol-biodiesel-diesel). The addition of castor oil-derived biodiesel (COME) containing a high proportion of methyl ricinoleate (C18:1 OH) is an attractive approach in order to i) reduce the use of first generation biodiesel derived from edible sources, ii) balance the reduction in viscosity and lubricity of ethanol-diesel blends due to the high viscosity and excellent lubricity of methyl ricinoleate.
Technical Paper

The Comparative Study of Gasoline and n-butanol on Spray Characteristics

2014-10-13
2014-01-2754
n-butanol has been recognized as a promising alternative fuel for gasoline and may potentially overcome the drawbacks of methanol and ethanol, e.g. higher energy density. In this paper, the spray characteristics of gasoline and n-butanol have been investigated using a high pressure direct injection injector. High speed imaging and Phase Doppler Particle Analyzer (PDPA) techniques were used to study the spray penetration and the droplet atomization process. The tests were carried out in a high pressure constant volume vessel over a range of injection pressure from 60 to 150 bar and ambient pressure from 1 to 5 bar. The results show that gasoline has a longer penetration length than that of n-butanol in most test conditions due to the relatively small density and viscosity of gasoline; n-butanol has larger SMD due to its higher viscosity. The increase in ambient pressure leads to the reduction in SMD by 42% for gasoline and by 37% for n-butanol.
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