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Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible with different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a poppet valve train.

This work was concerned with evaluation of the performance and emissions of potential future biofuels during advanced spark ignition engine operation. The fuels prepared included three variants of gasoline, three gasoline-ethanol blends and a gasoline-butanol fuel altogether covering a range of oxygen mass concentrations and octane numbers to identify key influencing parameters. The combustion of the fuels was evaluated in a turbocharged multi-cylinder direct fuel injection research engine equipped with a standard three-way catalyst and an external EGR circuit that allowed use of either cooled or non-cooled EGR. The engine operating effects studied at both part and boosted high load conditions included fuel injection timing and pressure, excess air tolerance, EGR tolerance and spark retard limits. A number of blends were also mapped at suitable sites across the European drive cycle under downsized engine conditions.

Morphology plays an important role in determining behaviour and impact of soot nanoparticles, including effect on human health, atmospheric optical properties, contribution to engine wear, and role in marine ecology. However, its nanoscopic size has limited the ability to directly measure useful morphological parameters such as surface area and effective volume. Recently, 3D morphology characterization of soot nanoparticles via electron tomography has been the subject of several introductory studies. So-called ‘3D-TEM’ has been posited as an improvement over traditional 2D-TEM characterization due to the elimination of the error-inducing information gap that exists between 3-dimensional soot structures and 2-dimensional TEM projections. Little follow-up work has been performed due to difficulties with developing methodologies into robust high-throughput techniques.

Natural Gas (NG) is currently a cost effective substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. Dual-Fuel engines substitute NG in place of diesel for decreased NOx and soot emissions, but suffer from high engine-out methane (CH4) emissions. Premixed Dual-Fuel Combustion (PDFC) is one method of decreasing methane emissions and simultaneously improving engine efficiency while maintaining low NOx and soot levels. PDFC utilizes an early diesel injection to adjust the flammability of the premixed charge, promoting more uniform burning of methane. Engine experiments were carried out using a NG and diesel HD single cylinder research engine. Key speeds and loads were explored in order to determine where PDFC is effective at reducing engine-out methane emissions over Conventional Dual-Fuel which uses a single diesel injection for ignition.

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.

The work examined the practicality of converting a modern production 6 cylinder 7.7 litre heavy-duty diesel engine for flex dual-fuel operation with ammonia as the main fuel. A small amount of diesel fuel (pilot) was used as an ignition source. Ammonia was injected into the intake ports during the intake stroke, while the original direct fuel injection equipment was retained and used for pilot diesel injection. A bespoke engine control unit was used to control the injection of both fuels and all other engine parameters. The aim was to provide a cost-effective retrofitting technology for existing heavy-duty engines, to enable eco-friendly operation with minimal carbon emissions. The tests were carried out at a baseline speed of 600 rpm for the load range of the engine (10-90%), with minimum pilot diesel quantity and as high as 90% substitution ratio of ammonia for diesel fuel.

This paper presents results from an experimental programme researching the in-cylinder conditions necessary to obtain homogenous CAI (or HCCI) combustion in a 4-stroke engine. The fuels under investigation include three blends of Unleaded Gasoline, a 95 RON Primary Reference Fuel, Methanol, and Ethanol. This work concentrates on establishing the CAI operating range with regard to Air/Fuel ratio and Exhaust Gas Re-circulation and their effect on the ignition timing, combustion rate and variability, Indicated thermal efficiency, and engine-out emissions such as NOx. Detailed maps are presented, defining how each of the measured variables changes over the entire CAI region. Results indicate that the alcohols have significantly higher tolerance to dilution than the hydrocarbon fuels tested. Also, variations in Gasoline blend have little effect on any of the combustion parameters measured.

We present a computational tool to develop an exhaust gas recirculation (EGR) - air-fuel ratio (AFR) operating range for homogeneous charge compression ignition (HCCI) engines. A single cylinder Ricardo E-6 engine running in HCCI mode, with external EGR is simulated using an improved probability density function (PDF) based engine cycle model. For a base case, the in-cylinder temperature and unburned hydrocarbon emissions predicted by the model show a satisfactory agreement with measurements [Oakley et al., SAE Paper 2001-01-3606]. Furthermore, the model is applied to develop the operating range for various combustion parameters, emissions and engine parameters with respect to the air-fuel ratio and the amount of EGR used. The model predictions agree reasonably well with the experimental results for various parameters over the entire EGR-AFR operating range thus proving the robustness of the PDF based model.

The work was concerned with the use of exhaust gas recirculation to minimise CO2 and pollutant emissions over a wide operating range in a multi-cylinder research engine. Under part-load conditions a combination of internal and external EGR was used to invoke controlled auto ignition combustion and improve fuel consumption. Outside the CAI regime, small additional fuel savings could be made by employing reduced EGR rates in spark ignition combustion mode. At boosted high load conditions a comparison of excess fuel, excess air and cooled external EGR charge dilution was made. It was apparent that cooled EGR was a more effective suppressant of knock than excess air, with combustion phasing further advanced towards the optimum and improved combustion stability achieved over a wider operating range. The full load emissions reduction potential of EGR was also demonstrated, with emissions of CO2 reduced by up to 17% and engine-out HC and CO decreased by up to 80%.

This work was concerned with increasing the attainable load during gasoline controlled auto-ignition combustion in a multi-cylinder direct fuel injection research engine. To extend the peak output under naturally aspirated conditions it proved favourable to combine internal and external exhaust gas recirculation under stoichiometric fuelled conditions. During turbocharged high load operation it was beneficial in terms of fuel economy to dilute the charge with a combination of internally re-circulated exhaust gases and excess air. Replacing a proportion of these diluents with externally re-circulated burned gases appeared to facilitate lower emissions of HC and CO. The highest load generated via boost was limited by increasing peak in-cylinder pressure and falling gas exchange efficiency. Regardless, the use of boost increased the load at which CAI could be invoked without lean NOx after-treatment.

Characterization of soot nanoparticle morphology can be used to develop understanding of nanoparticle interaction with engine lubricant oil and its additives. It can be used to help direct modelling of soot-induced thickening, and in a more general sense for combatting reductions in engine efficiency that occur with soot-laden oils. Traditional 2D transmission electron microscopy (TEM) characterization possesses several important shortcomings related to accuracy that have prompted development of an alternative 3D characterization technique utilizing electron tomography, known as 3D-TEM. This work details progress made towards facilitating semi-automated image acquisition and processing for location of structures of interest on the TEM grid. Samples were taken from a four cylinder 1.4 L gasoline turbocharged direct injection (GTDI) engine operated in typically extra-urban driving conditions for 20,284 km, with automatic cylinder deactivation enabled.

Vegetable oils have been seen as promising surrogates to petroleum diesel in compression ignition internal combustion engines, showing similar performance and combustion characteristics of the fossil fuel. Nevertheless, the use of straight (crude) vegetable oil (SVO) is unfavorable due to its high viscosity, which affects the Sauter Mean Diameter of fuel spray and, consequently, fuel-air mixing process, resulting in incomplete combustion. The SVO heating, as well as transesterification and blending with diesel or additives, are some of the techniques to reduce its viscosity and enable its use. Of these the most simple and direct is the heating and was used in this paper to evaluate the performance and emissions of a diesel engine fueled with preheated soybean oil (PSO) by electrical resistances. The experiments were carried out in a single cylinder four-stroke compression ignition engine with mechanical fuel injection.

The work was concerned with applying cooled EGR for improved high load fuel economy and reduced pollutant emissions in a turbocharged gasoline engine. While the thermodynamic benefits of EGR were clear, challenges remain to bring the technique to market. A comparison of pre and post compressor EGR supply indicated that post-compressor routing allowed higher compressor efficiencies to be maintained and hence reduced compressor work as the mass flow of EGR was increased. However, with this post-compressor routing, attaining sufficient EGR rate was not possible over the required operating map. Furthermore, at higher engine speeds where the pre-turbine exhaust pressure was greater than the intake plenum pressure, the timing of peak in-cylinder pressure was not as readily advanced towards the optimum.

An experimental study has been carried out with the end goal of minimizing engine-out methane emissions with Premixed Micro Pilot Combustion (PMPC) in a natural gas-diesel Dual-Fuel™ engine. The test engine used is a heavy-duty single cylinder engine with high pressure common rail diesel injection as well as port fuel injection of natural gas. Multiple variables were examined, including injection timings, exhaust gas recirculation (EGR) percentages, and rail pressure for diesel, conventional Dual-Fuel, and PMPC Dual-Fuel combustion modes. The responses investigated were pressure rise rate, engine-out emissions, heat release and indicated specific fuel consumption. PMPC reduces methane slip when compared to conventional Dual-Fuel and improves emissions and fuel efficiency at the expense of higher cylinder pressure.

Using Exhaust Gas Recycling (EGR) on internal combustion engines enables the reduction of emissions with a low or even no cost to the engine efficiency at part-load operation. The charge dilution with EGR can even increase the engine efficiency due to de-throttling and reduction of part load pumping losses. This experimental study proposed the use of late exhaust valve closure (LEVC) to achieve internal EGR (increased residual gas trapping). A naturally aspirated single cylinder direct injection spark ignition engine equipped with four electro-hydraulic actuated valves that enabled full valve timing and lift variation. Eight levels of positive valve overlap (PVO) with LEVC were used at the constant load of 6.0 bar IMEP and the speed of 1500 rpm. The results have shown that later exhaust valve closure (EVC) required greater intake pressures to maintain the engine load due to the higher burned gases content. Hence, lower pumping losses and thus higher indicated efficiency were obtained.

A combination of internal and external exhaust gas recirculation has been used to increase the attainable load in a multi-cylinder engine operated in gasoline controlled auto-ignition. The amount of residual gas trapped in the cylinder was adjusted via the negative valve overlap method. The flow of externally re-circulated exhaust gas was varied using a typical production level valve. Under stoichiometric fuelling conditions, the highest output achieved using internal exhaust gas was limited by excessive pressure rise and unacceptable levels of knock. Introducing additional external exhaust gas was found to retard ignition, reduce the rate of heat release and limit the peak knocking pressure. In turn, an increase in engine load of 20-65% was achieved, with greatest benefit governed by combustion stability limits and realised at lower engine speeds.

This work was concerned with use of two-stage cam profile switching to transition between SI and CAI combustion in a multi-cylinder direct fuel injection research engine. In order to achieve robust combustion mode changes, it proved necessary to switch the inlet and exhaust bank of tappets independently of one another. Practical issues addressed to improve tappet response included minimising tappet oil circuit dead volumes and reducing the oil pressure difference before and after a switch. When switching from SI to CAI combustion, it was possible to avoid misfire and operate the engine in a mixed-mode form of combustion. In addition, it was demonstrated that supplementary external EGR could be used to minimise transient peak knocking pressures during such transitions. Differences in overall engine noise levels during SI and CAI have also been qualified and some possible solutions are discussed.