The term 'dual fuel' refers to a compression ignition engine where a small quantity of diesel fuel called the pilot is used to ignite a second gaseous fuel which is the primary energy source. The motivation to use dual fuel has traditionally been economic, as the primary fuel is often less expensive than the distillate fuel it replaces. However, some benefits in terms of the reduced emissions of smoke and oxides of nitrogen (NOx) can also be achieved. In this research, a small, direct injection diesel engine was converted to dual fuel operation. This engine is typical of those used in stationary power generation applications. A review of literature revealed that whilst performance and emissions trends were well established for indirect injection engines, little research had been conducted on a direct injection engine. In particular, this class of small, high speed industrial engine had been somewhat neglected, partly because they have been subject to less stringent emissions legislation than their automotive counterparts. By performing a detailed investigation ' into the errors and assumptions that have a bearing on the three zone technique, it was possible to challenge some previous assumptions regarding the dual fuel combustion process. Namely, the theory that the pilot bums in two separate initial stages was found to be a deficiency of previous analysis techniques and therefore incorrect. It was found that as the proportion of the gaseous fuel was increased, the combustion process retained similar characteristics and magnitudes of mass burned to diesel until all but the highest equivalence ratios. At this point, the premixed and diffusion burning periods merged, but continued to show a fundamental dependence on the pilot ignition and the combustion processes were never independent of the pilot. The range of equivalence ratios over which the transition between the two patterns occurs is firstly a function of the primary fuel, and secondly a function of the operating conditions (such as in cylinder temperature). It is proposed that the dual fuel combustion process is better described as a diesel combustion process with a modified diffusion burning period that results from the gaseous fuel concentration and type. By using this explanation, it was identified that the emissions characteristics of the engine could be modified through the use of a second fuel. The primary fuel can reduce the initial mass burning rates (to reduce NOx) and simultaneously elevated the diffusion burning rates (to reduce smoke emissions). This provides an alternative, beneficial means by which the classic diesel NOx-Particulate trade-off can be manipulated. Butane was found to be unsuitable for this type of engine, and propane consistently yielded the best performance and emissions trends. Additionally, it was found that the addition of small quantities of methane or propane can result in disproportionately large reductions in smoke and NOx without the penalty of increased carbon monoxide and unburned hydrocarbons.

Large 2-stroke marine diesel engines burn high sulphur content residual fuel. The sulphur converts to aqueous sulphuric acid, H2SO4, and condenses on the cylinder liner surface, where it causes corrosive attack when not neutralised by the high alkaline reserve in the lubricant. Cylinder liner wear and deposit formation are observed to reflect poor lubricant distribution, surface temperature and sulphur fuel content, which all influence acid concentration. Currently neglected by the industry, is the catalysing action of H2SO4 on lubricant degradation and the rheology of entrained droplets in the oil film, which was the motivation for this study. To understand the basic interaction of H2SO4 with the lubricant film, the Saturated hydrocarbon squalane, C30H62, was chosen as a simple model oil in addition to fully formulated lubricants and their corresponding API Group I base oils. Interfacial tension between oil and aqueous solutions of H2SO4 was measured. Contact angles of aqueous solutions of H2SO4 immersed in C30H62 on piston ring chrome coating compared to grey cast iron cylinder liner material were measured. Fully formulated lubricant and API Group I base oil was used pure and emulsified with H2SO4 to lubricate a piston ring/ cylinder contact on a Plint TE77 Tribometer. The main analytical techniques were the light microscope, SEM/EDX, XPS, FTIR, laser diffraction particle size characterisation, white-light-interferometer and viscometer. Inter facial tension measurements of aqueous H2SO4 against C30H62 reveal a close relationship with the dissociation of H2SO4, which is also reflected by the formation of bituminous emulsions with API Group I base oil when above 40% w/wH2SO4 and formation of solids when above 80% w/wH2SO4 and high temperatures of around 120–165°C or long storage times. For pure water, the contact angles were found to be large while they were small for concentrated sulphuric acid. Contact angles on chrome coating were bigger than on grey cast iron. Advancing contact angles were larger than static and receding contact angles, which was expected. During the TE77tests,the degradation temperature of the base oil was lowered when in contact with H2SO4 from 250 to 80°C for oxidation, from 300 to 170°C for nitration and from 300 to 120°C for deposit formation. Over all the appearance of the surfaces improved when sulphuric acid was added to both, the API Group I base oil and the fully formulated lubricant.

Over the last decade, the diesel engine has made dramatic progress in its performance and market penetration. However, in order to meet future emissions legislations, Nitrogen Oxide (NOx) and particulate matter (PM) emissions will need to be reduced simultaneously. Nowadays researchers are focused on different combustion modes like homogeneous charge compression ignition (HCCI) combustion and premixed charge compression ignition (PCCI) which have a great potential for both low soot and low NOx. In order to achieve these combustion modes, different injection strategies have been investigated. This study investigates the effects of split injection strategies with high levels of Exhaust Gas Recirculation (EGR) on combustion performance and emissions in a high speed direct injection optical diesel engine. The investigation is focused on the effects of split injections at different injection pressures, injection timings and dwell angles using base diesel and biodiesel fuels. The effect of fuel properties has been also investigated as an attempt to reduce regulated exhaust emissions in diesel engines. Performance, emissions and combustion characteristics have been examined for two different biodiesel fuels, namely BTL 50 and BTL 46. A Ricardo Hydra single cylinder optical engine was used in which conventional experimental methods like cylinder pressure data, heat release analysis and exhaust emissions analysis were applied. Optical techniques like direct spray and combustion visualization were applied by means of a high speed imaging system with a copper vapour laser illumination system. A high-speed two-colour system has been developed and implemented to obtain in-cylinder diesel combustion temperature and soot measurements to gain better understanding of the mixture formation and combustion processes. This investigation concludes that the split injection strategies show potential to achieve low emissions combustion.

This thesis describes work undertaken at the University of Brighton on a rapid compression machine based on a two-stroke diesel engine (Proteus) with an optical head to allow observation of the fuel spray. A long-tube, rate of injection rig was used to measure the injection rate of the fuel injection system. Quantification of cyclic variation and rate of injection were carried out for single and multiple-injection strategy. For multiple-injections, it was found that the injected mass of the first of the split was approximately 19% less than that of the single injection strategy for the same injection duration. The second split reduction was less than 4% in comparison to the single injection strategy. The transient response of the fuel injection equipment was characterised and compared with steady-state behaviour. The characteristics of the Proteus rig in terms of trapped air mass and transient incylinder temperature were investigated and quantified. The effect of in-cylinder temperature, density and pressure, as well as injection pressure on the characteristics of spray formation, for single and multi-hole nozzles were investigated using high speed video cameras. Cycle-to-cycle and hole-to-hole variations for multi-hole nozzles were investigated and attributed to uneven fuel pressure distribution round the needle seat, and subsequent cavitation phenomena. Simultaneous Planar Laser Induced Fluorescence (PLIF) and Mie scattering techniques were used to investigate spray formation and vapour propagation for multihole nozzles for single and multiple-injection strategy. The multiple injection work focused on the effect of dwell period between each injection. Two different modes of flow were identified. These are described as 'wake impingement' and 'cavity mode wake effect', resulting in increased tip velocity of the second split spray. The increase in tip velocity depended on dwell period and distance downstream of the nozzle exit. The maximum increase was calculated at 17 m/s. A spray pattern growth for the second of the split injections, the 'exceed type' was identified, resulting from an increase in tip penetration due to air entrainment of the first split and propagation into the cooler vapour phase from the first split. The effect of liquid core length near the nozzle exit was investigated using modified empirical correlations and the evolution of the discharge coefficient obtained from rate of injection measurements. The results showed increased injection pressure and increased in-cylinder gas pressure reduce both break-up length and break-up time. Penetration was modelled using conservation of mass and momentum of the injected fuel mass. The input to the numerical model was the measured transient rate of injection. The model traced the centre-of-mass of the spray and was validated against PLIF data for centre-of-mass. Overall, the same value of modelling parameters gave good agreement for single and split injection strategy.

An experimental investigation of post-start cold idling behaviour has been carried out on a modern single-cylinder HPCR DI light duty diesel engine with a low compression ratio of 15.5:1 at temperatures between 10 and -20°C. The trend toward lower compression ratios from more common values of around 22:1 a few years ago has resulted in lower compression pressures and temperatures, which negatively affects cold idle operation. Improvements in cycle-by-cycle stability of indicated work output through fuel injection strategy and glow plug temperature changes have been explored. This is important to improve NVH and the consumer’s perception of vehicle quality. The key effects on heat release characteristics have been identified and the associated impact on stability discussed. High speed imaging of ignition in a combustion bomb has been used to aid interpretation of engine results. Up to four pilot injections placed in advance of the main have been used. Shorter separation between pilots and pilot-to-main improves stability independent of the number of pilot injections and extends the range of main injection timings to meet target stability of 10% or lower at -20°C. Increasing the number of pilot injections was effective in stabilising combustion at all investigated soak temperatures at fuelling levels producing indicated work required to match friction and ancillary demands. Stability can be susceptible to deterioration at moderate soak temperatures because fuelling demand is relatively low. If a high number of pilot injections are to be avoided to reduce potential wear, then increasing main injection quantity is an effective method to stabilise combustion for a lower pilot number strategy but any increase above target load has to be harnessed by additional ancillary devices. Very high glow plug temperatures of up to 1200°C were examined using a smaller diameter tip ceramic type design. Stable combustion cannot be achieved through higher glow plug temperatures alone. A temperature of 1000°C, which can be achieved using a low voltage metallic type, is adequate to stabilise combustion when combined with a triple-pilot strategy at sub-zero temperatures. The best stability is achieved using 1200°C, which can only be achieved using a more expensive ceramic type, in combination with a triple-pilot strategy producing the desirable target of ~5% or below; the effects are not mutually exclusive. At high glow plug temperatures and using three or four pilot injections, stability improved with warmer soak temperatures. At -5°C, stability was relatively poor when one or two pilots were used irrespective of glow plug temperature. A high premixed contribution to main combustion is associated with improved stability. Minimum threshold values are necessary to stabilise combustion: ~25 J/° at -20°C, ~20 J/° at -5°C and only ~10 J/° at 10°C. A higher number of pilot injections raises pilot induced combustion and improves mixture distribution. These effects subsequently increase the premixed combustion and help sustain a strong main development with less variability. This benefit is maximised when using hotter glow plug temperatures raising IMEPg magnitude and reducing variation.

This thesis describes research undertaken to establish the advantages and disadvantages of using high pressure common rail fuel injection systems with multiple injection capabilities. The areas covered are detailed as follows. Oscillations in the rail pressure due to the opening of the injector can affect the quantity of fuel injected in subsequent injection events. The source of these oscillations has been investigated. A method of damping or reducing the oscillations has been defined and was applied. This successfully reduced the level of unpredictability of the quantity of injected fuel in subsequent injection events. A relationship between needle lift, injection pressure and the quantity of fuel injected was established. The effects of fuel injection parameters (main injection timing, split main separation and ratio) and engine operating parameters (boost pressure and EGR level) on emissions formations and fuel economy have been investigated at five operating points. Design of Experiments techniques were applied to investigate the effect of variables on pollutant emissions and fuel consumption. The sensitivity and linearity of responses to parameter changes have been analysed to assess the extent to which linear extrapolations will describe changes in smoke number (FSN) and oxides of nitrogen (NOx); and which parameters are the least constricting when it comes to adjustments of parameter settings on the FSN-NOx map. Comparing results for split main and single injection strategies at the five operating conditions shows that split main injection can be exploited to reduce NOx or FSN values at all conditions and both NOx and FSN simultaneously at high load conditions. The influence of changing engine speed and brake mean effective pressure (BMEP) on FSN and NOx emissions with given fixed values of parameter settings has been investigated. This established how much of the operating map could be covered by discrete calibration settings. Finally the variation in parameter settings required to maintain fixed FSN and NOx values across the operating map, near the optimum trade-off on the FSN-NOx map, was analysed. Combining the information gained from the individual investigations carried out highlighted some techniques that can be used to simplify the calibration task across the operating map, while also reducing the amount of experimental testing required.

Στο πλαίσιο της παρούσας διπλωματικής εργασίας έγινε μια εκτεταμένη διερεύνηση μέσω προσομοίωσης της συμπεριφοράς ενός συστήματος αποτελούμενο από μηχανή Diesel , σύγχρονη μηχανή εκτύπων πόλων ως γεννήτρια και ασύγχρονη μηχανή δακτυλιοφόρου δρομέα ως κινητήρα. Παρουσιάστηκαν όλες οι τεχνικές που χρησιμοποιούνται στην μοντελοποίηση ενός τέτοιου συστήματος στο περιβάλλον του προγράμματος SIMULINK του MATLAB. Διερευνήθηκαν όλα τα φαινόμενα που λαμβάνουν χώρα κατά την εκκίνηση ενός τέτοιου συστήματος καθώς και οι πιο χαρακτηριστικοί τύποι βραχυκυκλωμάτων που μπορούν να παρουσιαστούν κατά την λειτουργία ενός τέτοιου συστήματος, τόσο κατά την μεταβατική κατάσταση λειτουργίας (Transient state), όσο και κατά την μόνιμη κατάσταση λειτουργίας (Steady state). Ακόμη μελετήθηκε η συμπεριφορά του συστήματος κατά την παύση της λειτουργίας του. / -

L’hybridation électrique de la chaîne de traction automobile est l’une des solutions adoptées pour respecter les règlementations futures sur ses émissions. La stratégie de supervision de la chaîne de traction hybride répartit la puissance produite par le moteur à combustion interne et la machine électrique. Elle répond habituellement à un problème d’optimisation où l’objectif est de réduire la consommation de carburant mais nécessite à présent d’y ajouter les émissions polluantes. La chaîne de dépollution, placée à l’échappement du moteur, permet de diminuer la quantité de polluants émise dans l’atmosphère. Cependant, elle n’est efficace qu’à partir d’un seuil de température, et dépend de la chaleur apportée par les gaz d’échappement du moteur thermique. La première partie de ce travail est donc consacrée à la modélisation de la consommation énergétique et des émissions polluantes de la chaine de traction hybride. La modélisation de l’efficacité de la chaîne de dépollution est réalisée selon deux contextes. Le modèle zéro-dimensionnel est adapté aux contraintes de calcul de la commande optimale. Le modèle unidimensionnel associé à un estimateur d’état permet d’être embarqué et calculé en temps réel. À partir de ces travaux, la seconde partie de cette thèse déduit des stratégies de supervision à l’aide de la théorie de la commande optimale. Dans un premier cas, le principe de Bellman permet de calculer la commande optimale d’un véhicule hybride Diesel selon des critères de supervision ayant plus ou moins connaissance de l’efficacité de la chaîne de dépollution des émissions de NOX. Dans un second cas, une stratégie issue du Principe du Minimum de Pontryagin, embarquée sur un véhicule hybride essence, fonctionnant en temps réel et calibrée selon deux paramètres est proposée. L’ensemble de ces travaux est validé expérimentalement au banc moteur et montre une réduction significative des émissions polluantes pour une faible pénalité de carburant. / Powertrain hybridization is a solution that has been adopted in order to conform to future standards for emissions regulations. The supervisory strategy of the hybrid powertrain divides the power emitted between the internal combustion engine and the electric machine. In past studies, this strategy has typically responded to an optimization problem with the objective of reducing consumption. However, in addition to this, it is now necessary to take pollutant emissions into account as well. The after-treatment system, placed in the exhaust of the engine, is able to reduce pollutants emitted into the atmosphere. It is efficient from a certain temperature threshold, and the temperature of the system is dependent on the heat brought by the exhaust gas of the engine. The first part of this dissertation is aimed at modelling the energy consumption and pollutant emissions of the hybrid powertrain. The efficiency model of the after-treatment system is adapted for use in two different contexts. The zero-dimensional model conforms to the constraints of the optimal control calculation. The one-dimensional model associated with a state estimator can be embedded in a vehicle and calculated in real time. From this work, the second part of this dissertation deduces supervisory strategies from the optimal control theory. On the one hand, Bellman’s principle is used to calculate the optimal control of a Diesel hybrid vehicle using different supervisory criteria, each having more or less information about the after-treatment system efficiency over NOX emissions. On the other hand, a strategy from Pontryagin’s minimum principle, embedded in a gasoline hybrid vehicle, running in real time and calibrated with two parameters, is proposed. The whole of this work is validated experimentally on an engine test bed and shows a significant reduction in pollutant emissions for a slight fuel consumption penalty.