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The effect on the intake flow field, air fuel mixing processes, thermodynamic performance and emissions output has been investigated for a range of valve operating profiles. A standard speed load point of 2000 rpm and 2.7 bar IMEP720° has been reached by throttling the intake whilst running standard cam profiles, by early closing of both inlet valves (EIVC) and by early closing of each inlet individually to generate bulk swirl motions within the cylinder. Data has been recorded at stoichiometric air fuel ratios for both direct injection and port fuelled operation. The valve profiles have been applied to two single cylinder homogeneous gasoline direct injection (GDI) spark ignition engines, developed to investigate the potential of controlling engine load by limiting the inducted air mass using fully variable valve timing (FVVT) to reduce pumping losses at part load.

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.

This paper describes the application of a new technique, Phosphorescent Particle Tracking (PPT), to the visualisation of gas flow streams in the cylinder of an engine flow rig. This technique uses small phosphorescent tracer particles suspended in the air-stream to provide evidence of the gas flow profile as they are carried away from the plane of excitation. A two colour version of the technique is also presented. This latter technique is shown to have the potential to reveal the interaction or degree of stratification of two flow streams within the cylinder.

One of the latest advancements in injector technology is laser drilling of the nozzle holes. In this context, the spray formation and atomisation characteristics of gasoline, ethanol and 1-butanol were investigated for a 7-hole spark eroded (SE) injector and its ‘direct replacement’ Laser-drilled (LD) injector using optical techniques. In the first step of the optical investigation, high-speed spray imaging was performed in a quiescent injection chamber with global illumination using diffused Laser light. The images were statistically analyzed to obtain spray penetration, spray tip velocity and spray ‘cone’ angles. Furthermore, droplet sizing was undertaken using Phase Doppler Anemometry (PDA). A single spray plume was isolated for this analysis and measurements were obtained across the plume at a fixed distance from the nozzle exit.

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.

Numerical simulations are performed to investigate the effects of droplet size distribution on fuel transport and air-fuel mixing in a gasoline direct-injection (GD-I) engine. The engine grid was generated using the K3PREP grid generator and the simulations were carried out using the KIVA-3V Release 2 code. Three size distribution functions were considered, namely the Chi-squared (χ2) and two Rosin-Rammler functions with dispersion parameter, q of 3.5 and 7.5 (RRq=3.5 and RRq=7.5). A new subroutine, which arranges the fuel droplets into a spherical cloud of droplets, was developed to allow the in-cylinder placement of fuel droplets with different droplet size distribution. Two cases of intake valve timing were considered. Results of the simulation showed droplet size distribution to affect fuel dispersion under the influence of the in-cylinder gas flows.

International obligations to reduce carbon dioxide emissions and requirements to strengthen security of fuel supply, indicate a need to diversify towards the use of cleaner and more sustainable fuels. Hydrogen has been recommended as an encouraging gaseous fuel for future road transportation since with reasonable modifications it can be burned in conventional internal combustion engines without producing carbon-based tailpipe emissions. Direct injection of hydrogen into the combustion chamber can be more preferable than port fuel injection since it offers advantages of higher volumetric efficiency and can eliminate abnormal combustion phenomena such as backfiring. The current work applied a fully implicit computational methodology along with the Reynolds-Averaged Navier-Stokes (RANS) approach to study the mixture formation and combustion in a direct-injection spark-ignition engine with hydrogen fuelling.

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 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.

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.

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.

Underhood thermal management is an important area in new vehicle design, consuming substantial engineering resources and requiring extensive access to costly prototype vehicles throughout a development programme. Simulation-based design methods and computational tools have been validated for steady-state investigations of forced flows within engine bays. However, transient analyses with a long timescale, such as the simulation of natural convective flow under the hood during heat soak, are still unfeasible due to the high computing requirements. The present paper intends to define a reliable computation procedure that will enable time-marching Computational Fluid Dynamic (CFD) simulations to be performed with significantly reduced CPU time usage. The performance of the proposed methodology was evaluated through model comparison with a fully transient CFD solution.

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).

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.

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.

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.

A significant amount of harmful emissions pass unreacted through catalytic after-treatment devices for IC engines before the light-off temperature is reached, despite the high conversion efficiency of these systems in fully warm conditions. Further tightening of fleet targets and worldwide emission regulations will make a faster catalyst light-off to meet legislated standards hence reduce the impact of road transport on air quality even more critical. This work investigates the effect of adding hydrogen (H2) at levels up to 2500 ppm into the exhaust gases produced by combustion of various oxygenated C2-, C4- and renewable fuel molecules blended at 20 % wt/wt with gasoline on the light-off performance of a commercially available three-way catalyst (TWC) (0.61 L, Pd/Rh/Pt - 19/5/1, 15g). The study was conducted on a modified naturally aspirated, 1.4 L, four-cylinder, direct-injected, spark-ignition engine.

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.

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.

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.