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Our earlier experimental study has shown that exhaust unburnt hydrocarbon emissions from spark-ignition engines can be reduced effectively by using in-cylinder catalysts on the surface of the piston top-land crevice. In order to improve the understanding of the process and mechanism by means of which unburnt hydrocarbon emissions are reduced, a phenomenological mathematical model was developed for catalytic oxidation processes in the piston-ring-pack crevice. This paper describes in details the modelling of the processes of the gas flow, mass diffusion and reaction kinetics in the crevices. The flow in the crevices is assumed to be isothermal and at the temperature of the piston crown surface. The overall rate of reaction is calculated using expressions for mass diffusion for laminar flows in channels and a first-order Arrhenius-type expression for catalytic reaction kinetics of hydrocarbon oxidation over platinum.

The work was concerned with experimental study of the turbulent flame development process of ethanol fuels in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access and operated at typical stoichiometric part-load conditions. High-speed natural light (or chemiluminescence) imaging and simultaneous in-cylinder pressure data measurement and analysis were used to understand the fundamental influence of both low and high ethanol content on turbulent flame propagation and subsequent mass burning. Causes for the difference in cyclic variations were evaluated in detail, with comparisons made to existing burning velocity correlations where available.

Heavy duty hydrogen (H2) internal combustion engines (ICEs), typically conversions from base diesel engines, can experience significant deterioration of combustion efficiency with enleanment despite relative engine stability due in part to non-optimized combustion chamber geometry for spark ignited (SI) combustion. This causes un-combusted H2 to “slip” into the exhaust largely undetected since it is not a typically measured exhaust species. In this study, several implications of H2 slip in H2 ICEs are explored. The sensitivity of air fuel ratio (AFR) measurement to H2 slip is discussed. The challenge this poses for closed-loop transient controls and the impact on nitrogen oxides (NOx) emissions are also shown. Finally, test results from an H2 ICE using an active pre-chamber highlight the improvement in combustion efficiency and transient stability relative to a baseline SI engine.

Tumble and swirl motions in the cylinder of a four-valve SI engine with production type cylinder head were investigated using a cross-correlation digital Particle Image Velocimetry (PIV). Tumble motion was measured on the vertical symmetric plane of the combustion chamber. Swirl motion was measured on a plane parallel to the piston crown with one of intake ports blocked. Large-scale flow behaviours and their cyclic variations were analysed from the measured two-dimensional velocity data. Results show that swirl motion is generated at the end of the intake stroke and persists to the end of the compression stroke. Tumble vortex is produced in the early stage of the compression stroke and distorted in the late stage of the stroke. The cyclic variation of swirl motion is noticeable. The cyclic variation in tumble dominated flow field is much greater.

Knock in gasoline engines at higher loads is a significant constraint on torque and efficiency. The anti-knock property of a fuel is closely related to its research octane number (RON). Ethanol has superior RON compared to gasoline and thus has been commonly used to blend with gasoline in commercial gasolines. However, as the RON of a fuel is constant, it has not been used as needed in a vehicle. To wisely use the RON, an On-Board Separation (OBS) unit that separates commercial gasoline with ethanol content into high-octane fuel with high ethanol fraction and a lower octane remainder has been developed. Then an onboard Octane-on-demand (OOD) concept uses both fuels in varying proportion to provide to the engine a fuel blend with just enough RON to meet the ever changing octane requirement that depends on driving pattern.

The goal of this research was to study and quantify the effect of exhaust valve timing and residual gas dilution on in-cylinder flow patterns, flame propagation and heat release characteristics in a spark ignition engine. Experiments were carried out in a recently developed single cylinder optical engine. Particle image velocimetry (PIV) was applied to measuring and evaluating the in-cylinder flow field. Detailed analysis of flame images combined with heat release data was presented for several engine operating conditions, giving insight into the combustion process in terms of visible flame area and flame expansion speed. Results from PIV measurement indicates that the limited alteration of the in-cylinder bulk flow could be observed with the variation of exhaust valve timing. The in-cylinder fluctuating kinetic energies and their Coefficient of Variations (COVs) decrease with the advance of the exhaust valve timing.

In recent years, in order to develop more efficient and cleaner gasoline engines, a number of new engine operating strategies have been proposed and many have been studied on different engines but there is a lack of comparison between various operating strategies and alternative fuels at different SI modes. In this research, a single cylinder direct injection gasoline engine equipped with an electro-hydraulic valve train system has been commissioned and used to study and compare different engine operation modes. In this work, the fuel consumption, gaseous and particulate emissions of gasoline and its mixture with ethanol (E15 and E85) were measured and analysed when the engine was operated at the same load but with different load control methods by an intake throttle, reduced intake valve duration, and positive overlap.

A novel approach was proposed and investigated to reduce unburned hydrocarbon emissions from spark-ignition engines using in-cylinder catalysts. The unburned hydrocarbons in spark-ignition engines arise primarily from sources near the combustion chamber walls, such as flame quenching at the entrance of crevice volumes and at the combustion chamber wall, and the absorption and desorption of fuel vapour into oil layers on the cylinder wall. The proximity of these sources of unburned hydrocarbons to the wall means that they can be reduced significantly by simply using in-cylinder catalysts on the combustion chamber walls, in particular on the surfaces of the crevice volumes. A platinum-rhodium coating was deposited on the top and side surfaces of the piston crown, and its effects on the engine combustion and emission characteristics were examined in this experimental investigation.

This work was concerned with study of lubricant introduced directly into the combustion chamber and its effect on pre-ignition and combustion in an optically accessed single-cylinder spark ignition engine. The research engine had been designed to incorporate full bore overhead optical access capable of withstanding peak in-cylinder pressures of up to 150bar. An experiment was designed where a fully formulated synthetic lubricant was deliberately introduced through a specially modified direct fuel injector to target the exhaust area of the bore. Optical imaging was performed via natural light emission, with the events recorded at 6000 frames per second. Two port injected fuels were evaluated including a baseline commercial grade gasoline and low octane gasoline/n-heptane blend. The images revealed the location of deflagration sites consistently initiating from the lubricant itself.

With an increasing global awareness of the need to conserve fuel resources and reduce carbon dioxide emissions, the automotive sector has been seeking gains in engine efficiency. One such method for achieving these gains on a spark ignition (SI) engine platform is through lean burn operation. Ultra-lean operation (λ>2) has demonstrated the ability to increase thermal efficiency and significantly reduce emissions of nitrogen oxides (NOx) due primarily to lower mean gas temperatures. Turbulent Jet Ignition (TJI), a pre-chamber-based combustion system, is a technology that enables ultra-lean operation. TJI is also an effective knock mitigation system due to the distributed nature of main chamber ignition, resulting in rapid burn rates. Pre-chamber combustors such as that utilized in TJI have been studied extensively for decades, but the interaction of the combustion events between the two chambers is not well understood.

A programme of work is being undertaken to improve the performance of a spark-ignited natural gas engine, that has been converted from a diesel engine. The aim of this work is to reduce the fuel consumption and NOx emissions. All experimental data and predictions refer to full throttle operation at 1500 rpm. The work to be reported here will include baseline tests that have been used to calibrate a two-zone combustion model. Particularly important are the predictions of the NOx emissions. The simulation has then been used to predict the effects of using: a higher compression ratio, and a faster burn combustion system. The design philosophy of the resulting fast burn combustion system is discussed, and some preliminary results are presented. There will be a discussion of the ignition parameters that affect the lean burn operation, and the effect of the spark plug gap position is discussed in the context of results from a phenomenological model of turbulent combustion.

A numerical study was performed to elucidate the link between cyclic combustion variations in spark-ignition engines and instabilities in the non-linear processes occurring during the combustion. The instabilities in combustion were investigated by examining the response of a two-zone phenomenological combustion models to small deviations of mixture and flow conditions in the cylinder, such as the turbulence intensity at ignition, the overall equivalent ratio and the local equivalent ratio around the ignition site. The predicted combustion characteristics were validated and in good agreement with experimental data obtained from a single-cylinder research engine. The study suggested that the main deficiency of combustion in spark-ignition engines is the point-source ignition: it gives rise to slow development of initial flame; variations of the intermittent combustion process can occur when initial conditions at the ignition site are not repeatable from cycle to cycle.

A novel experimental technique was used to investigate the in-cylinder air-fuel ratio excursions of a port-injected spark-ignition engine during load and fuel transients. This involved sampling directly from the engine cylinder using a fast flame ionisation detector (FID) system throughout an engine transient test. All tests were conducted with the coolant at the normal operating temperature of 90°C. The research engine used was a 1.6ltr four-cylinder multi-point fuel injection spark-ignition (SI) engine with four-valves-per-cylinder, with sequential injection and an electronic management system. The engine transient involved a rapid throttle opening within about 15msec. Various load steps were investigated at 2000rev/min along with the effect of altering the type of fuel injector.

Progressively more stringent efficiency and emissions regulations for internal combustion engines have led to growing interest in advanced combustion concepts for spark ignition engines. MAHLE Jet Ignition® (MJI) is one such concept which enables ultra-lean (λ > ~1.6) combustion via air dilution. This pre-chamber-based combustion system has demonstrated highly efficient lean operation, producing efficiencies competitive with those of advanced compression ignition concepts. Compared to a traditional spark ignition engine, the additional degrees of freedom associated with Jet Ignition introduce further complexity when optimizing the system for peak efficiency throughout the engine map. The relationship between operating condition and the lambda at which peak efficiency occurs for a Jet Ignition engine has been presented in prior work by the authors.

Controlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange process The engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation. In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively.

Natural gas is a promising alternative fuel as it is affordable, available worldwide, has high knock resistance and low carbon content. This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas at several air to fuel ratios and speed-load operating points. In addition, Turbulent Jet Ignition optical images are compared to the baseline spark ignition images at the world-wide mapping point (1500 rev/min, 3.3 bar IMEPn) in order to provide insight into the relatively unknown phenomenon of Turbulent Jet Ignition combustion. Turbulent Jet Ignition is an advanced spark initiated pre-chamber combustion system for otherwise standard spark ignition engines found in current passenger vehicles. This next generation pre-chamber design simply replaces the spark plug in a conventional spark ignition engine.

Increasingly stringent global fuel economy and carbon dioxide (CO2) legislation for light duty passenger cars has created an interest in unconventional operating modes. One such mode in spark ignition (SI) gasoline engines is lean combustion. While lean operation in SI engines has previously demonstrated the ability to reduce fuel consumption, the degree of enleanment capability of the system is limited by increasingly unstable combustion in the lean region, particularly for homogeneous lean approaches. MAHLE Jet Ignition® (MJI) is a pre-chamber-based combustion system that extends this lean limit beyond the capabilities of modern SI engines by increasing the ignition energy present in the system. This allows the engine to exploit the benefits of homogeneous ultra-lean (λ > ∼1.6) combustion, namely reduced fuel consumption and reduced emissions of nitrogen oxides (NOx). Pre-chamber combustors such as that utilized in MJI have been studied extensively for decades.

Alternative combustion modes for spark ignition engines, such as homogeneous lean combustion, have been extensively researched in transportation and large stationary power applications due to their inherent emissions and fuel efficiency benefits. However, these types of approaches have not been explored for small engines (≤ 30 kW), as the various applications for these engines have historically had significantly different market demands and less stringent emissions requirements. However, going forward, small engines will need to incorporate new technologies to meet increasingly stringent regulatory guidelines. One such technology is jet ignition, enables lean combustion via air dilution through the use of a pre-chamber combustor.

This paper presents the development of an engine simulation program for SI engines and its application to a two-stage expansion cycle. The two-stage expansion analysis is performed using the engine simulation, where a sudden expansion much faster than the normal expansion takes place during the expansion stroke. The changes in NO emissions and knock tolerance of the resulting new engine cycle are investigated for the same compression ratio. The changes in NO emissions and specific fuel consumption through increasing the compression ratio in order to return to the same amount of work done within the cycle are also studied.

The work was concerned with visualisation of the charge homogeneity and cyclic variations within the planar fuel field near the spark plug in an optical spark ignition engine fitted with an outwardly opening central direct fuel injector. Specifically, the project examined the effects of fuel type and injection settings, with the overall view to understanding some of the key mechanisms previously identified as leading to particulate formation in such engines. The three fuels studied included a baseline iso-octane, which was directly compared to two gasoline fuels containing 10% and 85% volume of ethanol respectively. The engine was a bespoke single cylinder with Bowditch style optical access through a flat piston crown. Charge stratification was studied over a wide spectrum of injection timings using the Planar Laser Induced Fluorescence (PLIF) technique, with additional variation in charge temperature due to injection also estimated when viable using a two-line PLIF approach.