Dissertations / Theses on the topic 'DICI ENGINE'

The cold start catalyst warm-up operation is seen as one of the most important modes in Direct Injection Spark Ignition (DISI) Engine operation. When the catalyst is cold the engine out emissions become the tailpipe out emissions, so it is vital for the catalyst to obtain its working temperature as quickly as possible. A very high exhaust temperature can be achieved with a very retarded ignition - the engine can be made to operate at no load with a close to wide open throttle. With a retarded ignition, a split injection strategy has been shown to improve combustion stability which is critical for the trade-off between tailpipe emissions and vehicle idle stability. The spray guided DISI engine has a multi- hole injector centrally located in the chamber with the spark plug. For catalyst heating operation, the first injection occurs during induction, which forms a relatively well mixed but lean mixture in the cylinder before ignition, and the second injection occurs close to a retarded ignition, which produces a stratified fuel rich mixture in the central region of the combustion chamber near the spark plug. Combustion initialization is found to be sensitive to spark plug protrusion and orientation, injector orientation and 2nd injection timing relative to ignition. High tension current and voltage measurements have been taken in order to characterize the effect of the 2nd injection timing on both the breakdown and the glow phase of the arc discharge. Both phases are shown to be influenced by the timing of the 2nd injection. The richer mixture causes the breakdown voltage to increases while the airflow entrained in the 2nd injection has been shown to stretch the spark and in the worst case extinguish it prematurely. In-cylinder spray imaging by Mie scattering has been taken with frame rates up to 6000 fps, with high speed video photography of chemiluminescence and soot thermal radiation. Tests have studied the effect of the spark plug orientation and injector orientation, with timing sweeps for the phasing of the second injection. The images show interaction of a fuel jet with the earth electrode, stretching of the arc, variable location for the start of combustion and significant cycle-by-cycle variations with the same operating point leading to normal combustion, slow combustion and misfiring cycles. Spectroscopic measurements have confirmed the presence of OH *, CH * and C2*; emissions lines, and their relative magnitude compared to soot radiation. Filtering for CH * has been used with a photo-multiplier tube. These signals show the arc discharge, the delay between the arc and the kernel growth and (depending on the timing of the 2nd injection) small kernels which do not subsequently fully develop and can cause misfiring cycles. Unburned hydrocarbon emissions have been measured with a fast-response FID, so that emissions can be related to: misfiring cycles, slow burning cycles (0 < GMEP <0.5), and normal cycles. These measurements show that only the misfiring cycles lead to significant unburnt hydrocarbon emissions. The misfire mechanism depends on the timing of the 2nd injection. When the 2nd injection ends at the spark, no kernel is seen for a misfiring cycle. However, a kernel is shown to grow in the lean background mixture indicating that the misfire mechanism, when the 2nd injection ends close to the spark, is that the local air/fuel ratio is too rich for the onset of combustion. However, when the 2nd injection is significantly retarded from the spark a different misfire mechanism is present. A small kernel is shown to exist between the spark and the arrival of the fuel from the 2nd injection. For the misfiring cycle, this kernel is extinguished early, possibly due to an interaction between the kernel and the 2nd injection.

The currently reported thesis 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% (E10) and 85% (E85) 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. Overall, both gasoline-ethanol fuels generally exhibited a higher degree of stratification, albeit at least partly alleviated with elevated rail pressures. Under both warm and cold liner conditions the E10 fuel showed clear evidence of fuel droplets persisting up until ignition. Interestingly, with late injection timing the repeatability of the injection was superior (statistically) with higher ethanol content in the fuel, which may have been associated with the higher charge temperatures aiding control of the evaporation of the main mass of alcohol. The findings were corroborated by undertaking a comprehensive study of the influence of varying fuel type and injection settings on thermodynamic performance and engine-out emissions during firing operation, with additional gas exchange effects also influencing the optimum fuel injection timings.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 155-160).
Due to their advantages in higher fuel efficiency and torque compared to conventional port fuel injection (PFI) engines, direct injection spark ignition (DISI) engines have become dominant in gasoline-fueled engines. However, DISI engines have a significant drawback in particulate matter (PM) emission: the PM emission of DISI engines is at least an order of magnitude higher than that of PFI engines. The objective of this study is to investigate PM emission in DISI engines, mainly focusing on particulate number (PN) emission. The study aims to assess, respectively, the plausible PM formation mechanisms: non-fuel originated sources (e.g., lubricant), flame propagation in rich mixture and the pyrolysis of the vapor from liquid fuel film. Through a series of experiments, it has been found that non-fuel contribution is less important than the other two mechanisms. For all operating conditions, the absolute amount of the non-fuel contribution is much smaller than the total emission. In case of PM generated by flame propagation in rich mixture, there is a threshold air-fuel equivalence ratio below which PM starts to form rapidly. The threshold is influenced by the combustion temperature. PM starts to form at lower equivalence ratio when the combustion temperature was lower. Contrary to the PM generated from flame propagation in fuel-rich mixture case, that from the liquid fuel film is suppressed by lowering the combustion temperature. Transmission electron microscopy (TEM) imaging shows that the sizes of primary particles and agglomerated particles become larger as engine load increases, but particulates from different mechanisms have different morphology.
by Changhoon Oh.
Ph. D.

Particulate number (PN) standards in current and future emissions legislation pose a challenge for designers and calibrators during the warm-up phases of cold direct injection spark ignition (DISI) engines. To achieve catalyst light-off conditions in the shortest time, engine strategies are often employed that inherently use more fuel to attain higher exhaust temperatures. These can lead to the generation of locally fuel-rich regions within the combustion chamber and hence the formation and emission of particulates. To meet these emissions requirements, further understanding of the DISI in-cylinder processes during cold-start are required. This thesis investigates the effect of cooling an optical research engine to temperatures as low as -7°C, one of the legislative test conditions. A high-speed 9 kHz optical investigation of the in-cylinder combustion and fuel spray along with in-cylinder pressure measurements was completed with the engine motored and fired at 1500 rpm during combustion conditions that were essentially homogeneous and stoichiometric. Results showed significant differences between the flame growth structures at various operating temperature conditions with the notable presence of fuel-rich regions, which are understood to be prominent areas of particulate formation. Measured engine performance parameters such as indicated mean effective pressure (IMEP) and mass fraction burned (MFB) times correlated with the observed differences in combustion characteristics and flame growth speed. It was shown that flash boiling of the fuel spray was present in the fully heated engine case and significantly reduced the penetration of the spray plume and the likelihood of piston crown and cylinder liner impingement. The flow and combustion processes of a transient production cold start-up strategy were analysed using high-speed particle image velocimetry (HSPIV). Results highlighted a broad range of flame structures and contrasting flame stoichiometry occurring at different times in the start-up process. Turbulent flow structures were identified that have an effect on the fuel spray development and combustion process as well as providing a path for cold-start emissions reduction. PN and transient hydrocarbon (HC) emissions were measured at cold conditions to further elucidate the effect of operating temperature and correlate emissions data with in-cylinder measurements. A clear link between the quantity and size range of particulate and HC emissions and operating temperature was shown and the precise in-cylinder location of HC emissions, caused by fuel impingement, was inferred from the HC emissions data.

Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 81-83).
In an effort to build internal combustion engines with both reduced brake-specific fuel consumption and better emission control, engineers developed the Direct Injection Spark Ignition (DISI) engine. DISI engines combine the specific higher output of the spark ignition engine, with the better efficiency of the compression ignition engine at part load. Despite their benefits, DISI engines still suffer from high hydrocarbon, NO2 and particulate matter (PM) emissions. Until recently, PM emissions have received relatively little attention, despite their severe effects on human health, related mostly to their size. Previous research indicates that almost 80% of the PM is emitted during the first few minutes of the engine's operation (cold-start-fast-idling period). A proposed solution for PM emission reduction is the use of fuel blends with ethanol. The present research experimentally measures the effect of ethanol content in fuel on PM formation in the combustion chamber of a DISI engine during the cold-start period. A novel sampling system has been designed and combined with a Scanning Mobility Particle Sizer (SMPS) system, in order to measure the particulate matter number (PN) concentration 15 cm downstream from the exhaust valves of a DISI engine, for a temperature range between 0 and 40"C, under low load operation. Seven gasohol fuels have been tested with the ethanol content varying from 0% (EO) up to 85% (E85). For E10 to E85, PN modestly increases when the engine coolant temperature (ECT) is lowered. The PN distributions, however, are insensitive to the ethanol content of the fuel. The total PN for EQ is substantially higher than for the gasohol fuels, at ECT below 20'C. However, for ECT higher than 20'C, the total PN values (obtained from integrating the PN distribution from 15 to 350 nm) are approximately the same for all fuels. This sharp change in PN from EQ to E10 is confirmed by running the tests with E2.5 and E5; the midpoint of the transition occurs at approximately E5. Because the fuels' evaporating properties do not change substantially from EQ to E10, the significant change in PN is attributed to the particulate matter formation chemistry.
by Iason Dimou.
Nav.E.and S.M.

There is currently considerable interest in new engine technologies to assist in the improvement of fuel economy and the reduction of carbon dioxide emissions from automotive vehicles. Within the current automotive market, legislative and economic forces are requiring automotive manufacturers to produce high performance engines with a reduced environmental impact and lower fuel consumption. To meet these targets, further understanding of the processes involved in in-cylinder combustion is required. This thesis discusses the effect of fuel spray structure, flame propagation and turbulent flow on DISI engine combustion. To investigate these flow processes within the fired single cylinder Jaguar optical engine a number of optical measurement techniques have been used, including high speed laser sheet flow visualisation (HSLSFV) and high speed digital particle image velocimetry (HSDPIV). Results obtained from dual location flame imaging has provided further understanding of the relationship between flame growth, engine performance and cycle-to-cycle variation. Detailed correlation analysis between flame growth speed and engine performance parameters demonstrated that it is the flow conditions local to the spark plug at the time of spark ignition that have greatest influence on combustion. It was also demonstrated that further gains in engine performance and stability can be achieved by optimising the fuel injection timing. The temporal and spatial development of flow field structures within the pent-roof combustion chamber at the time of spark ignition were quantified using HSDPIV. Decomposition analysis of the raw velocity data enabled the relationship between specific scales of turbulent flow structure and engine performance parameters to be investigated. Correlations between the high frequency turbulence component and pressure derivatives are shown, demonstrating that it is the frequencies of motion >600 Hz that have the greatest influence on early flame development and therefore rate of charge consumption, engine performance and combustion stability. A series of double fuel injection strategies were devised to investigate the potential for using the fuel injection event to influence flow field structures within the cylinder. Results demonstrated that while the fuel injection event had limited impact on bulk flow structures, there was an increase in turbulence post fuel injection, depending on the timing of the second injection pulse. However, this advantage was not sustained throughout the compression stroke to have significant impact on combustion. The final stage of research investigated fuel spray structure, flame propagation and charge motion at fuel impingement locations, comparing a single and triple injection strategy. A triple injection strategy is proposed that results in an improvement in the levels of fuel impingement on combustion chamber walls and a reduction in the high luminosity regions within the flame. Consequently, adopting the multiple injection strategy highlighted the potential for reducing unburned HC emissions and soot formation within homogeneous charge DISI engines.

This work investigates through numerical simulation, the operation of a big bore direct fuel injection spark ignition engine, at part load under stratified operation. It evaluates fuel-air mixture preparation and combustion process with the adoption of detailed chemical kinetics mechanisms for both Isooctane and Ethanol, and applying adaptive mesh refinement to capture the turbulent flame brush. The investigation is split in 3 main parts. In the first part, with Isooctane as fuel, the impact of in-cylinder turbulence level induced by squish has shown that the attempt to isolate the squish ratio, maintaining the bowl shape, for the evaluated cases have led to a scenario not more appropriate for flame initiation and propagation for 2 of the 3 geometries. But the observations made during this initial stage have led to the proposal of a fourth geometry to improve the mixture formation and combustion process. As it was seen the combustion process was about 11.5 deg faster with the new piston bowl proposed. In the second part, still with Isooctane and maintaining the new proposed piston, evaluates the influence of two types of hollow cone fuel injectors, an inwardly and an outwardly opening types, where maintain fixed spark timing, the end of injection is varied and compared among the two cases, while targeting for the same gross IMEP output. The main results are that the outwardly opening injector case resulted in better fuel-air mixture preparation, even with a late end of injection. This led to higher combustion efficiency and lower unburned hydrocarbon, CO and soot emissions, while increasing NOx emissions. The 10-90% MFB burn duration is higher for the outwardly opening injector case. In the last part the outwardly opening spray injector from the previous part, but using Ethanol as fuel has shown that to attain the same IMEP level the injected fuel mass is increased with Ethanol, and with its higher latent heat of vaporization, the time required to have an ignitable fuel-air mixture more than doubled that for the Isooctane case. Another important effect of these is the excessive increase of THC emissions. The overall combustion duration was faster for the Ethanol, mainly as the last part of the combustion was almost twice as fast as for the Isooctane case. It may be a consequence of a more homogeneous fuel-air mixture cloud as the fuel has more time to diffuse as the EOI is more advanced. The in-cylinder charge cooling effect of Ethanol led to a reduction in the in-cylinder temperature, leading to a reduction in NOx formation. CO emissions was also lowered, which is maybe attributed to either the reduced chemical dissociation with the lower temperatures, or reduced fuel rich regions. The reduced fuel rich regions also explain the reason for lower soot emissions.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, June 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 43-44).
The United States consumes billions of gallons of gasoline per year, threatening national security and causing environmental problems. Research in automotive research aims to resolve such problems. Solutions include turbocharged direct injection, spark ignition (DISI) engines for higher output and efficiency. But this comes at the cost of greater concentrations of unburned hydrocarbons (UBHC) in the exhaust during cold start, when the catalytic converter is further away from the engine. The time the catalytic converter takes to heat to an optimum efficiency is longer. UBHC can also accumulate in the cylinder chambers and can be caused by quenching effects or poor mixing. A system was set up to determine the significance of mixing in producing high concentrations of UBHC. A GM 2009 LNF Ecotec was modified to run PFI and DISI under operating conditions representative of cold start for isopentane, and gasoline with varying concentrations of ethanol. Results were inconclusive, indicating no relationship between neither the UBHC count in the exhaust of increasing ethanol concentration, nor differences between PFI and DISI. To make test results more reliable, more ethanol containing fuel types should be tested, and a sweep of spark times should be assessed. The set up does provide a good foundation for further studies in mixing research.
by Sareena Avadhany.
S.B.

Direct Injection Spark Ignition has become popular within the automotive industry due to the flexibility in injection strategies. This, along with the introduction of novel fuels such as mixtures of ethanol or butanol with gasoline, requires new understanding of the air-fuel mixture preparation and combustion as fuel properties vary greatly. The motored engine flow field of an optical research engine was characterised using Laser Doppler Velocimetry and Particle Image Velocimetry and analysed regarding turbulence properties at the world wide mapping point. The intake flow effect on the spray of a pressure swirl injector was investigated using the base fuels gasoline, isooctane, ethanol and butanol. Furthermore, low percentage splash blended mixtures of 25 % ethanol and 16 % or 25 % butanol with the reference fuels were created and geometrical spray features were obtained from high speed imaging along with the droplet sizes using Phase Doppler Anemometry. Spray investigations were also under taken in a quiescent environment with a more modern spark eroded multi hole injector and its direct replacement featuring a novel Laser drilled nozzle. The results highlight the strong effect of the fuel type, where especially pure butanol showed largest difference to the baseline fuels in terms of shape along with a significant increase of the droplet size. Ethanol also showed an increase in droplet size but only small differences to gasoline’s spray shape at 80 bar or 120 bar fuel pressure into 0.5 bar or 1 bar ambient air at 20 °C, for fuel temperatures of 20 °C or 80 °C. The ethanol mixture was typically more similar to gasoline than the butanol blends. Thermodynamic parameters were derived using incylinder pressure analysis for stoichiometric (λ=1) and lean (λ=1.2). Additionally, high speed chemiluminescence imaging was used at gasoline’s maximum break torque spark timing, calculating flame radii, radius growth, roundness and centroid development. Further analysis was using flame tomography for better insight into the early stages after ignition and the flame front characteristics for the base fuels only. Overall, the analysis showed little difference between gasoline and the blends, but showed changes for the pure alcohols with typically much faster flame progression of ethanol and issues with the combustion of butanol at low engine temperatures. The tomography analysis returned similar flame structures for the pure fuels, what is confirmed by their location in combustion diagrams.

This research investigated a novel combustion system for gasoline direct injection spark ignition (DISI) engines. This combustion system burned an unthrottled, stoichiometric, homogenous charge at part load, in comparison to the unthrottled,lean, stratified charge burned by conventional DISI engines. Unthrottled homogeneous operation, enabled by the use of variable valve timing. allowed high fuel efficiencies to be achieved while addressing the particulate emissions, poor combustion stabilities and NOx after-treatment issues associated with stratified charge DISI engines, when compared to the port fuel injection (PFI) engines they are replacing. Experiments were performed to quantifY the bulk in-cylinder air motions, determine their effect on the fuel spray, and examine the resulting air-fuel mixture preparation of various early inlet valve closing (EIVC) and late inlet valve opening (LIVO) strategies that were suitable for controlling engine load under homogeneous engine conditions. A broad matrix of engine conditions has been investigated, with engine speeds ranging from idle (750 rpm) to 5000 rpm, and engine loads ranging from 2.7 bar indicated mean effective pressure (!MEP) to wide open throttle (WOT). Particle Image Velocimetry (PIV) was used to record mean in-cylinder flow fields in the tumble and swirl planes for a range of engine conditions and valve profiles. This included measurements at higher engine speeds (3500rpm) than previously published. Air flows in the difficult-to-access cylinder head were measured with Laser Doppler Anemometry (LDA) and the effect of these air flows on the fuel spray produced by a latest generation multi-stream fuel injector was investigated with Mie imaging. The resulting mixture preparation was then investigated over a crank angle period ranging from the start ofinjection (SOl) to the time of spark with Laser Induced Exciplex Fluorescence (LIE F). Supporting data from a thermodynamic sister engine with identical combustion chamber geometry was recorded at University College London. Unthrottled, homogeneous operation with low lift EIVC valve profiles improved engine fuel consumption by up to 20% compared to throttled operation with conventional, full-lift profiles. This was a consequence of a reduction in the throttling losses and improvements in air-fuel mixing. The intake air momentum was more significant than the fuel spray momentum from the injection system in determining the air-fuel mixing process. This resulted in engine performance being strongly affected by engine speed, intake valve lift and injection timing. The greatest benefits in ISFC occurred when only one of the two inlet valves was operated. This was attributed to an overall increase in the level ofin-cylinder swirl. However, the choice of which inlet valve was opened was critical, with greater gains occurring if the fuel spray from the centrally mounted injector was directed towards the spark plug than when the spray was directed away from the plug. EIVC combustion also exhibited significantly longer burn times than throttled operation. This was due to lower cylinder pressures that reduced the laminar flame speed and lower levels of turbulence around the spark plug at the time of ignition. Flame front measurements on the optical engine showed that during the longer early heat release phase (0-10% mass fraction burned), the flame kernel was transported away from the spark plug and towards the combustion chamber wall beneath the inlet valves. Investigations into the fuel mixture preparation using Laser Induced Exciplex Fluorescence (LIE F) demonstrated that, under high load conditions, a source of particulate emissions from PFI engines was large droplets in the vicinity of the spark plug around the time of ignition. These fuel rich regions were precursors in the generation of soot and were all but eliminated with direct injection fuelling strategies. Late Intake Valve Opening (LIVO) valve strategies generated a sub-atmospheric cylinder pressure of between 0.5 to 0.3bar (absolute). Spray images obtained under these conditions showed greater penetration of the fuel spray and a poorly defined spray cone boundary. Due to the increased momentum and increased shear forces of the inducted air, and the cylinder pressure falling below the saturation vapour pressure of some components of the gasoline fuel at the temperature of the mixture, flash evaporation of those components was seen to occur. The improvement in atomisation and faster burn rate with LIVO compensated to some extent for the increase in irrecoverable pumping work of this operating strategy over conventional EIVC. However, a practical disadvantage of LIVO was poor control of the trapped air mass, arising from the intake air momentum supercharging the engine cylinder at the conditions tested.

Cette étude introduit une nouvelle approche appelée Bivariate 2D-EMD pour séparer le mouvement organisé à grande échelle, soit la composante basse fréquence de l’écoulement des fluctuations turbulentes, soit la composante haute fréquence dans un champ de vitesse instantané bidimensionnel.Cette séparation nécessite un seul champ de vitesse instantané contrairement aux autres méthodes plus couramment utilisées en mécanique des fluides, comme le POD. La méthode proposée durant cette thèse est tout à fait appropriée à l’analyse des écoulements qui sont intrinsèquement instationnaires et non linéaires comme l'écoulement dans le cylindre lorsque le moteur fonctionne dans des conditions transitoires. Bivariate 2D-EMD est validé à travers différents cas test, sur un écoulement turbulent homogène et isotrope (THI) expérimental, qui a été perturbé par un tourbillon synthétique de type Lamb-Ossen, qui simule le mouvement organisé dans le cylindre. Enfin, Il est appliqué sur un écoulement expérimental obtenu dans un cylindre et les résultats de la séparation d'écoulement sont comparés à ceux basés sur l'analyse POD. L’évolution d’écoulement dans le cylindre pendant le fonctionnement du moteur transitoire, c’est à dire une accélération du régime moteur de 1000 à 2000tr/min en différentes rampes, sont mesurée en utilisant de PIV 2D-2C haute cadence. Les champs de vitesse sont obtenus dans le plan de tumble dans un moteur un moteur GDI mono-cylindre transparent et forment une base de données nécessaire pour valider les résultats de simulation numérique
This study introduces a new approach called Bivariate 2D-EMD to separate large-scale organizedmotion i.e., flow low frequency component from random turbulent fluctuations i.e., high frequency onein a given in-cylinder instantaneous 2D velocity field. This signal processing method needs only oneinstantaneous velocity field contrary to the other methods commonly used in fluid mechanics, as POD.The proposed method is quite appropriate to analyze the flows intrinsically both unsteady and nonlinearflows as in in-cylinder. The Bivariate 2D-EMD is validated through different test cases, by optimize itand apply it on an experimental homogeneous and isotropic turbulent flow (HIT), perturbed by asynthetic Lamb-Ossen vortex, to simulate the feature of in-cylinder flows. Furthermore, it applies onexperimental in-cylinder flows. The results obtained by EMD and POD analysis are compared. Theevolution of in-cylinder flow during transient engine working mode, i.e., engine speed acceleration from1000 to 2000 rpm with different time periods, was obtained by High speed PIV 2D-2C. The velocityfields are obtained within tumble plane in a transparent mono-cylinder DISI engine and provide a database to validate CFD

Thesis (M.S.)--University of Wisconsin--Madison, 2003.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 150-152).

The present dissertation has investigated the influence of injection parameters on air/fuel mixture and combustion processes in a DISI engine, through advanced diagnostics. It is possible to distinguish three parts of the work: the spray macroscopic parameters characterization, the spray break-up investigation and the study of the effects of injection timing and duration on the combustion process. In the first stage, the influence of injection pressure and duration on the fuel mass rate and the spray morphology has been analysed. A fuel injection rate meter based on the Bosch Tube principle has provided useful information about the time resolved behaviour of the delivered mass highlighting both transient, such as needle lift and nozzle closing operation, and quasi steady stages of the injection event. 2D Mie-scattering imaging and Particle Image Velocimetry technique have been used for characterizing the liquid spray morphology in terms of tip penetration, cone angle and velocity vector distribution. Even if the injection parameters affect the overall spray geometry, the characterization of the inner structure of the spray is fundamental for featuring the atomization phenomena which influence the fuel - air interaction. Therefore, Phase Doppler Anemometry (PDA) and Laser Doppler Velocimetry (LDV) have been applied for providing information about the velocity and size of droplets. Trials have been performed at different injection pressures and distances from the nozzle, along two different axes: the first one corresponding to the jet axis, the second one on the jet edge. Especially at the higher injection pressure, accurate tests have been possible only at a certain distance from the nozzle, where the spray is more dilute and the laser beam can cross the jet core. For this reason X-ray absorption measurements have been performed in order to investigate high-dense regions of fuel sprays, immediately downstream of the nozzle, providing quantitative measurements of the fuel. X-rays penetrate the dense part of fuel spray because of its weak interaction with the hydrocarbon chain due to their low atomic number. X-ray radiography and tomography have been used to investigate the spray core and reconstruct the 3D inner structure. The information about the spray development has been used to optimize the injection strategies of an optically accessible DISI engine operating at mid load condition, at a fixed speed of 2000 rpm. UV-visible imaging has been performed on the engine for investigating the influence of the injection duration and timing on the flame front propagation, while natural emission spectroscopy has been applied to characterize the formation and the evolution of the main compounds featuring the spark ignition and combustion processes. Exhaust emission measurements (HC, CO and NOx) have been correlated with pressure related data and optical results.