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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.

Recent pressures on vehicle manufacturers to reduce their average fleet levels of CO2 emissions have resulted in an increased drive to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO2 output of each vehicle. The most popular choice for spark-ignition engines has been the blending of ethanol with gasoline, where the ethanol is derived either from agricultural or cellulosic sources such as sugar cane, corn or decomposed plant matter. However, other fuels, such as butanol, have also arisen as potential candidates due to their similarities to gasoline, e.g. higher energy density than ethanol. To extract the maximum benefits from these new fuels through optimized engine design and calibration, an understanding of the behaviour of these fuels in modern engines is necessary.

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.

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.

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.

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.

Hydrogen has been largely proposed as a possible fuel for internal combustion engines. The main advantage of burning hydrogen is the absence of carbon-based tailpipe emissions. Hydrogen's wide flammability also offers the advantage of very lean combustion and higher engine efficiency than conventional carbon-based fuels. In order to avoid abnormal combustion modes like pre-ignition and backfiring, as well as air displacement from hydrogen's large injected volume per cycle, direct injection of hydrogen after intake valve closure is the preferred mixture preparation method for hydrogen engines. The current work focused on computational studies of hydrogen injection and mixture formation for direct-injection spark-ignition engines. Hydrogen conditions at the injector's nozzle exit are typically sonic.

Current developments in fuels and emissions regulations are resulting in increasingly severe operating environment for the injection system. Formation of deposits within the holes of the injector nozzle or on the outside of the injector tip may have an adverse effect on overall system performance. This paper provides a critical review of the current understanding of the main factors affecting deposit formation. Two main types of engine test cycles, which attempt to simulate field conditions, are described in the literature. The first type involves cycling between high and low load. The second involves steady state operation at constant speed either at medium or high load. A number of influences on the creation of deposits are identified. This includes fouling through thermal condensation and cracking reactions at nozzle temperatures of around 300°C. Also the design of the injector holes is an influence, because it can influence cavitation.

A key objective of this research was to develop an interface device to enable visualization of in-cylinder events within a production SI engine operating at normal speeds and loads, without the need for engine modifications. The device was designed to utilize the existing spark plug hole and to be capable of providing in-cylinder illumination, image transmission and a source of ignition. This technical paper presents the results of the initial evaluation of the device. The evaluation of the durability of the device, in terms of its ability to operate as a spark plug and its permissible operating range is presented. In addition, images of events in the cylinder captured using the device are provided.

Extensive literature exists on spray development, mixing and combustion regarding engine modeling and diagnostics using single-component and model fuels. However, often the variation in data between different fuels, particularly relating to spray development and its effect on combustion, is neglected or overlooked. By injecting into a quiescent chamber, this work quantifies the differences in spray development from a multi-hole direct-injection spark-ignition engine injector for two single-component fuels (iso-octane and n-pentane), a non-fluorescing multi-component model fuel which may be used for in-cylinder Laser Induced Fluorescence experiments, and several grades of pump gasoline (with and without additives). High-speed recordings of the sprays were made for a range of fuel temperatures and gas pressures. It is shown that a fuel temperature above that of the lowest boiling point fraction of the tested fuel at the given gas pressure causes a convergence of the spray plumes.

Two-dimensional Mie-scattering and laser-induced fluorescence techniques were applied to investigate the effects of fuel composition on mixture formation within a firing direct-injection spark-ignition (DISI) engine. A comparison was made between the spray characteristics and in-cylinder fuel distributions resulting from the use of a typical multi-component gasoline (European specification premium-grade unleaded), a single-component research fuel (iso-octane), and a three-component research fuel (iso-pentane, iso-octane and n-nonane). Studies were performed at three different injection timings under cold and part-warm conditions. The results indicate that fuel composition affects both the initial spray formation and the subsequent mixture formation process. Furthermore, the sensitivity of the mixing process to the effects of fuel volatility was shown to depend on injection timing.

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.

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.

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.

This paper presents the results of an experimental study into the liquid sheet break-up mechanisms of high-pressure swirl atomizers of the type commonly used in direct-injection spark-ignition (DISI) engines. Sheet disintegration was investigated at two fuel pressures: 5 and 10 MPa, and three ambient back pressures: 50, 100 (atmospheric) and 200 kPa for a pre-production DISI injector. Microscopic images of the near-nozzle spray region were obtained with a high-speed rotating drum camera and copper vapour laser. For the range of conditions considered, the results show the initial break-up to occur in ‘perforated-sheet’ mode. A novel ‘void fraction’ analysis technique was applied to multiple images from the steady-state period of a single injection event in order to characterise and quantify details of the sheet break-up process. The sheet break-up lengths obtained by the authors were compared with the break-up lengths predicted by three commonly employed models from the literature.

Hydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NOX emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating.

Current developments in fuels and emissions regulations are resulting in an increasingly severe operating environment for diesel fuel injection systems. The formation of deposits within the holes or on the outside of the injector nozzle can affect the overall system performance. The rate of deposit formation is affected by a number of parameters, including operating conditions and fuel composition. For the work reported here an accelerated test procedure was developed to evaluate the relative importance of some of these parameters in a high pressure common rail fuel injection system. The resulting methodology produced measurable deposits in a custom-made injector nozzle on a single-cylinder engine. The results indicate that fuels containing 30%v/v and 100% Fatty Acid Methyl Ester (FAME) that does not meet EN 14214 produced more deposit than an EN590 petroleum diesel fuel.

The design of a Diesel injector is a key factor in achieving higher engine efficiency. The injector's fuel atomisation characteristics are also critical for minimising toxic emissions such as unburnt Hydrocarbons (HC). However, when developing injection systems, the small dimensions of the nozzle render optical experimental investigations very challenging under realistic engine conditions. Therefore, Computational Fluid Dynamics (CFD) can be used instead. For the present work, transient, Volume Of Fluid (VOF), multiphase simulations of the flow inside and immediately downstream of a real-size multi-hole nozzle were performed, during and after the injection event with a small air chamber coupled to the injector downstream of the nozzle exit. A Reynolds Averaged Navier-Stokes (RANS) approach was used to account for turbulence. Grid dependency studies were performed with 200k-1.5M cells.

This paper describes how the use of a computer model, followed by rig and engine testing, were employed to investigate the application of port throttles to a 4-valve SI engine. The results suggested that the throttling should be split between port and plenum throttles as this gave a faster bum rate than port throttling alone. It was argued that port throttling is most applicable to controlling the level of charge dilution on high-performance engines with large valve overlap periods. Port de-activation was also investigated, first separately, and then in combination with port throttles. Alone it increased the tolerance of the engine to EGR very significantly, and in combination it had the ability both to increase the EGR tolerance and to allow the use of a high-overlap camshaft.

There is a great deal of interest in new technologies to assist in reducing the CO2 output of passenger vehicles, as part of the drive to meet the limits agreed by the EU and the European Automobile Manufacturer's Association ACEA, itself a result of the Kyoto Protocol. For the internal combustion engine, the most promising of these include gasoline direct injection, downsizing and fully variable valve trains. While new types of spray-guided gasoline direct injection (GDI) combustion systems are finally set to yield the level of fuel consumption improvement which was originally promised for the so-called ‘first generation’ wall- and air-guided types of GDI, injectors for spray-guided combustion systems are not yet in production to help justify the added complication and cost of the NOx trap necessary with a stratified combustion concept.