Refine Your Search

Topic

Search Results

Technical Paper

An Investigation Into Transient Diesel Spray Development Using High Speed Imaging In A Novel Optical Pressure Chamber

2011-08-30
2011-01-1836
The fuel economy and emissions performance of a Diesel engine is strongly influenced by the fuel injection process. This paper presents early results of an experimental investigation into diesel spray development carried out in a novel in-house developed optical pressure chamber capable of operating at pressure up to 50 bar and temperatures up to 900 K. The spatial evolution of a diesel spray tends to experience many transitory macroscopic phenomena that directly influence the mixing process. These phenomena are not considered highly reproducible and are extremely short lived, hence recording and understanding these transient effects is difficult. In this study, high-speed backlight-illuminated imaging has been employed in order to capture the transient dynamics of a short signal duration diesel spray injected into incremental back pressures and temperatures reaching a maximum of 10 bar and 473 K respectively.
Technical Paper

Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays

2015-09-06
2015-24-2463
Flash-boiling of sprays may occur when a superheated liquid is discharged into an ambient environment with lower pressure than its saturation pressure. Such conditions normally exist in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or high fuel temperatures. The addition of novel high volatile additives/fuels may also promote flash-boiling. Fuel flashing plays a significant role in mixture formation by promoting faster breakup and higher fuel evaporation rates compared to non-flashing conditions. Therefore, fundamental understanding of the characteristics of flashing sprays is necessary for the development of more efficient mixture formation. The present computational work focuses on modelling flash-boiling of n-Pentane and iso-Octane sprays using a Lagrangian particle tracking technique.
Technical Paper

Characterisation of Spray Development from Spark-Eroded and Laser-Drilled Multi-Hole Injectors in an Optical DISI Engine and in a Quiescent Injection Chamber

2015-09-01
2015-01-1903
This paper addresses the need for fundamental understanding of the mechanisms of fuel spray formation and mixture preparation in direct injection spark ignition (DISI) engines. Fuel injection systems for DISI engines undergo rapid developments in their design and performance, therefore, their spray breakup mechanisms in the physical conditions encountered in DISI engines over a range of operating conditions and injection strategies require continuous attention. In this context, there are sparse data in the literature on spray formation differences between conventionally drilled injectors by spark erosion and latest Laser-drilled injector nozzles. A comparison was first carried out between the holes of spark-eroded and Laser-drilled injectors of same nominal type by analysing their in-nozzle geometry and surface roughness under an electron microscope.
Technical Paper

Characterization of Flame Development with Hydrous and Anhydrous Ethanol Fuels in a Spark-Ignition Engine with Direct Injection and Port Injection Systems

2014-10-13
2014-01-2623
This paper presents a study of the combustion mechanism of hydrous and anhydrous ethanol in comparison to iso-octane and gasoline fuels in a single-cylinder spark-ignition research engine operated at 1000 rpm with 0.5 bar intake plenum pressure. The engine was equipped with optical access and tests were conducted with both Port Fuel Injection (PFI) and Direct Injection (DI) mixture preparation methods; all tests were conducted at stoichiometric conditions. The results showed that all alcohol fuels, both hydrous and anhydrous, burned faster than iso-octane and gasoline for both PFI and DI operation. The rate of combustion and peak cylinder pressure decreased with water content in ethanol for both modes of mixture preparation. Flame growth data were obtained by high-speed chemiluminescence imaging. These showed similar trends to the mass fraction burned curves obtained by in-cylinder heat release analysis for PFI operation; however, the trend with DI was not as consistent as with PFI.
Technical Paper

Charge Stratification in a 4-Valve SI Engine Through Injection Into One Intake Port with Induced Axial Swirl Within the Cylinder

1997-10-01
972875
An arrangement of port - injected, stratified-charge, 4 - valve SI engine is proposed, in which fuel is injected in a thin column from an injector which is angled so that the fuel is deflected by one of the inlet valves onto the combustion chamber surface, at a position close to the central spark plug. The injection takes place towards the end of the induction stroke, and the injector is mounted to the side of one of the intake ports. The second intake port is deactivated at part load to establish an axial swirling motion to stabilise the fuel evaporating from the warm combustion chamber surface. Testing has been performed on a single - cylinder research engine to assess the extent of the stratification by measuring pre - flame hydrocarbon concentrations at various positions around the combustion chamber.
Technical Paper

Combining Unthrottled Operation with Internal EGR under Port and Central Direct Fuel Injection Conditions in a Single Cylinder SI Engine

2009-06-15
2009-01-1835
This experimental work was concerned with the combination of internal EGR with an early inlet valve closure strategy for improved part-load fuel economy. The experiments were performed in a new spark-ignited thermodynamic single cylinder research engine, equipped with a mechanical fully variable valvetrain on both the inlet and exhaust. During unthrottled operation at constant engine speed and load, increasing the mass of trapped residual allowed increased valve duration and lift to be used. In turn, this enabled further small improvements in gas exchange efficiency, thermal efficiency and hence indicated fuel consumption. Such effects were quantified under both port and homogeneous central direct fuel injection conditions. Shrouding of the inlet ports as a potential method to increase in-cylinder gas velocities has also been considered.
Technical Paper

Comparison between Unthrottled, Single and Two-valve Induction Strategies Utilising Direct Gasoline Injection: Emissions, Heat-release and Fuel Consumption Analysis

2008-06-23
2008-01-1626
For a spark-ignition engine, the parasitic loss suffered as a result of conventional throttling has long been recognised as a major reason for poor part-load fuel efficiency. While lean, stratified charge, operation addresses this issue, exhaust gas aftertreatment is more challenging compared with homogeneous operation and three-way catalyst after-treatment. This paper adopts a different approach: homogeneous charge direct injection (DI) operation with variable valve actuations which reduce throttling losses. In particular, low-lift and early inlet valve closing (EIVC) strategies are investigated. Results from a thermodynamic single cylinder engine are presented that quantify the effect of two low-lift camshafts and one standard high-lift camshaft operating EIVC strategies at four engine running conditions; both, two- and single-inlet valve operation were investigated. Tests were conducted for both port and DI fuelling, under stoichiometric conditions.
Technical Paper

Developing Low Gasoline Particulate Emission Engines Through Improved Fuel Delivery

2014-10-13
2014-01-2843
Particulate emissions are of growing concern due to health impacts. Many urban areas around the world currently have particulate matter levels exceeding the World Health Organisation safe limits. Gasoline engines, especially when equipped with direct injection systems, contribute to this pollution. In recognition of this fact European limits on particulate mass and number are being introduced. A number of ways to meet these new stringent limits have been under investigation. The focus of this paper is on particulate emissions reduction through improvements in fuel delivery. This investigation is part of the author's ongoing particulate research and development that includes optical engine spray and combustion visualisation, CFD method development, engine and vehicle testing with the aim to move particulate emission development upstream in the development process.
Journal Article

Development of a Fast-Acting, Time-Resolved Gas Sampling System for Combustion and Fuels Analysis

2016-04-05
2016-01-0791
Development of new fuels and engine combustion strategies for future ultra-low emission engines requires a greater level of insight into the process of emissions formation than is afforded by the approach of engine exhaust measurement. The paper describes the development of an in-cylinder gas sampling system consisting of a fast-acting, percussion-based, poppet-type sampling valve, and a heated dilution tunnel; and the deployment of the system in a single cylinder engine. A control system was also developed for the sampling valve to allow gas samples to be extracted from the engine cylinder during combustion, at any desired crank angle in the engine cycle, while the valve motion was continuously monitored using a proximity sensor. The gas sampling system was utilised on a direct injection diesel engine co-combusting a range of hydrogen-diesel fuel and methane-diesel fuel mixtures.
Technical Paper

Development of a Fuelling System to Reduce Cold-Start Hydrocarbon Emissions in an SI Engine

1996-05-01
961119
An air-assisted fuel vaporiser (AAFV), designed to replace the conventional fuelling system has been tested on a 3.0-litre development engine under simulated cold-Start conditions. Providing the cold engine with pre-vaporised fuel removed the need for an enriched mixture during start-up. Comparisons between the AAFV and standard fuelling systems were performed. Engine-out hydrocarbon (HC) exhaust emissions were measured during cold-start and the ensuing two minutes. Fuel spray characterisation was also conducted using a steady flow test rig designed to mimic inlet port conditions of air flow and manifold pressure over a wide range of engine operation.
Technical Paper

Effect of Impinging Airflow on the Near Nozzle Characteristics of a Gasoline Spray from a Pressure-Swirl Atomiser

2006-10-16
2006-01-3343
The effects of impinging airflow on the near nozzle characteristics of an inwardly opening, high pressure-swirl atomiser are investigated in an optically-accessed, steady-state flow rig designed to emulate the intake flow of a typical, side-injected, 4-valve gasoline direct-injection combustion system. The results indicate that the impinging airflow has a relatively minor effect on the initial break-up of the fuel spray. However, the secondary break-up of the spray, i.e. the break-up of liquid ligaments, the spatial distribution of droplets within the spray and the location of the spray within the cylinder are significantly affected by the impinging air.
Journal Article

Effect of the Molecular Structure of Individual Fatty Acid Alcohol Esters (Biodiesel) on the Formation of Nox and Particulate Matter in the Diesel Combustion Process

2008-06-23
2008-01-1578
Biodiesel is a renewable fuel which can be used as a direct replacement for fossil Diesel fuel as a calorific source in Diesel Engines. It consists of fatty acid mono-alkyl esters, which are produced by the trans-esterification reaction of plant oils with monohydric alcohols. The Plant oils and alcohols can both be derived from biomass, giving this fuel the potential for a sustainable carbon dioxide neutral life-cycle, which is an important quality with regard to avoiding the net emission of anthropogenic greenhouse gases. Depending on its fatty ester composition, Biodiesel can have varying physical and chemical properties which influence its combustion behaviour in a Diesel engine. It has been observed by many researchers that Biodiesel can sometimes lead to an increase in emissions of oxides of nitrogen (NOx) compared to fossil Diesel fuel, while emitting a lower amount of particulate mass.
Technical Paper

Effects of Fuel Injection Pressure in an Optically-Accessed DISI Engine with Side-Mounted Fuel Injector

2001-05-07
2001-01-1975
This paper presents the results of an experimental study into the effects of fuel injection pressure on mixture formation within an optically accessed direct-injection spark-ignition (DISI) engine. Comparison is made between the spray characteristics and in-cylinder fuel distributions due to supply rail pressures of 50 bar and 100 bar subject to part-warm, part-load homogeneous charge operating conditions. A constant fuel mass, corresponding to stoichiometric tune, was maintained for both supply pressures. The injected sprays and their subsequent liquid-phase fuel distributions were visualized using the 2-D laser Mie-scattering technique. The experimental injector (nominally a hollow-cone pressure-swirl design) was seen to produce a dense filled spray structure for both injection pressures under investigation. In both cases, the leading edge velocities of the main spray suggest the direct impingement of liquid fuel on the cylinder walls.
Technical Paper

Effects of Injection Timing on Liquid-Phase Fuel Distributions in a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

1998-10-19
982699
An experimental study was carried out to investigate the effects of fuel injection timing on the spatial and temporal development of injected fuel sprays within a firing direct-injection spark-ignition (DISI) engine. It was found that the structure of the injected fuel sprays varied significantly with the timing of the injection event. During the induction stroke and the early part of the compression stroke, the development of the injected fuel sprays was shown to be controlled by the state of the intake and intake-generated gas flows at the start of injection (SOI).The relative influence of these two flow regimes on the injected fuel sprays during this period was also observed to change with injection timing, directly affecting tip penetration, spray/wall impingement and air-fuel mixing. Later in the compression stroke, the results show the development of the injected fuel sprays to be dominated by the increased cylinder pressure at SOI.
Technical Paper

Effects of Injection Timing on the Exhaust Emissions of a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

1998-10-19
982700
A study to investigate the influence of fuel injection timing on exhaust emissions from a single-cylinder direct-injection spark-ignition (DISI) research engine was performed. Experimental results were obtained for carbon monoxide (CO), unburned hydrocarbon (HC), and oxides of nitrogen (NOx). Images showing the variation of liquid-phase fuel distribution with changing injection timing were obtained in a firing optically-accessed engine of similar design. A correlation between measured emissions and observed liquid-phase fuel distribution was performed. This correlation was supported by development of phenomenological models that permit explanation of the variation of CO, HC, and NOx emissions with changes in air-fuel mixture preparation.
Technical Paper

Effects on diesel combustion of the molecular structure of potential synthetic bio-fuel molecules

2007-09-16
2007-24-0125
Synthetic bio-fuels, which can be obtained through the gasification of biomass into synthesis gas and the subsequent catalytic reaction of the synthesis gas into liquid fuel molecules, could play a key-role in providing a sustainable source of automotive fuels during the coming decades. This paper presents an attempt to understand the effect of molecular structure of potential oxygenated synthetic bio-fuel molecules of different structure on the diesel combustion process in both stratified and homogeneous combustion modes. Specifically, the effects of molecular structure on the energy release rates, gaseous exhaust emissions and the sub-micron particulate matter distribution were examined. The experiments were carried out on a single-cylinder direct-injection diesel engine using a specially adapted common-rail fuel-system which allowed the injection of small single-molecule fuel samples at high pressure.
Technical Paper

Engine Testing of Dissolved Sodium Borohydride for Diesel Combustion CO2 Scrubbing

2014-10-13
2014-01-2729
Improvements in the efficiency of internal combustion engines and the development of renewable liquid fuels have both been deployed to reduce exhaust emissions of CO2. An additional approach is to scrub CO2 from the combustion gases, and one potential means by which this might be achieved is the reaction of combustions gases with sodium borohydride to form sodium carbonate. This paper presents experimental studies carried out on a modern direct injection diesel engine supplied with a solution of dissolved sodium borohydride so as to investigate the effects of sodium borohydride on combustion and emissions. Sodium borohydride was dissolved in the ether diglyme at concentrations of 0.1 and 2 % (wt/wt), and tested alongside pure diglyme and a reference fossil diesel. The sodium borohydride solutions and pure diglyme were supplied to the fuel injector under an inert atmosphere and tested at a constant injection timing and constant engine indicated mean effective pressure (IMEP).
Technical Paper

Fuel Spray Characterisation within an Optically Accessed Gasoline Direct Injection Engine Using a CCD Imaging System

1996-05-01
961149
A test facility was constructed at University College London to study fuel spray structure within a gasoline direct injection engine. The facility consisted of a single cylinder research engine with extensive optical access and a novel video imaging and analysis system. The engine used an experimental prototype 4-valve cylinder head with direct in-cylinder high pressure fuel injection, provided by a major automotive manufacturer. The fuel spray was illuminated using a pulsed copper-vapour laser. Results are presented that illustrate the spray behaviour within the fired research engine. A laser light sheet provided an insight into the inner spray cone behaviour.
Technical Paper

Investigating the Combustion and Emissions Characteristics of Biomass-Derived Platform Fuels as Gasoline Extenders in a Single Cylinder Spark-Ignition Engine

2017-10-08
2017-01-2325
The conversion of lignocellulosic biomass to liquid fuels presents an alternative to the current production of renewable fuels for IC engines from food crops. However, realising the potential for reductions in net CO2 emissions through the utilisation of, for example, waste biomass for sustainable fuel production requires that energy and resource inputs into such processes be minimised. This work therefore investigates the combustion and emission characteristics of five intermediate platform molecules potentially derived from lignocellulosic biomass: gamma-valerolactone (GVL), methyl valerate, furfuryl alcohol, furfural and 2-methyltetrahydrofuran (MTHF). The study was conducted on a naturally aspirated, water cooled, single cylinder spark-ignition engine. Each of the platform molecules were blended with reference fossil gasoline at 20 % wt/wt.
Journal Article

Large Eddy Simulation of an n-Heptane Spray Flame with Dynamic Adaptive Chemistry under Different Oxygen Concentrations

2015-04-14
2015-01-0400
Detailed chemical kinetics is essential for accurate prediction of combustion performance as well as emissions in practical combustion engines. However, implementation of that is challenging. In this work, dynamic adaptive chemistry (DAC) is integrated into large eddy simulations (LES) of an n-heptane spray flame in a constant volume chamber (CVC) with realistic application conditions. DAC accelerates the time integration of the governing ordinary differential equations (ODEs) for chemical kinetics through the use of locally (spatially and temporally) valid skeletal mechanisms. Instantaneous flame structures and global combustion characteristics such as ignition delay time, flame lift-off length (LOL) and emissions are investigated to assess the effect of DAC on LES-DAC results. The study reveals that in LES-DAC simulations, the auto-ignition time and LOL obtain a well agreement with experiment data under different oxygen concentrations.
X