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The interaction between a combusting diesel spray and a wall was studied by measuring the spray flame temperature time and spatially resolved. The influence of injection sequences, injection pressure and gas conditions on the heat transfer between the combusting spray and the wall was investigated by measuring the flame temperature during the complete injection event. The flame temperature was measured by an emission based optical method and determined by comparing the relative emission intensities from the soot in the flame at two wavelength intervals. The measurements were done by employing a monochromatic and non intensified high speed camera, an array of mirrors, interference filters and a beam splitter. The studies were carried out in the Chalmers High Pressure High Temperature (HP/HT) spray rig at conditions similar to those prevailing in a direct injected diesel engine prior to the injection of fuel.

In order to investigate the effects of split injection on emission formation and engine performance, experiments were carried out using a heavy duty single cylinder diesel engine. Split injections with varied dwell time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the selected parameters, other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezo-electric injector. To interpret the observed phenomena, engine CFD simulations using the KIVA-3V code were also made. The results show that reductions in NOx emissions and brake specific fuel consumption were achieved for short dwell times whereas they both were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of single injections.

The influence of ethanol blending in Diesel fuel on the spray and spray combustion characteristics was investigated by performing experiments in an optically accessible high-pressure / high-temperature spray chamber under non-evaporating, evaporating and combusting conditions. Three fuels were investigated: (1) Diesel - a European Diesel based on the EN590 standard; (2) E10 - a blend of Diesel containing 10% ethanol and 2% emulsion additive; and (3) E20 - a blend of Diesel containing 20% ethanol and 2% emulsion additive. A constant gas density of 24.3 kg/m3 was maintained under non-evaporating (30 °C, 21.1 bar), evaporating (350 °C, 43.4 bar), low combustion temperature (550 °C, 57.3 bar) and high combustion temperature (600 °C, 60 bar) conditions. A single-hole injector with a nozzle diameter of 0.14 mm was used and injection pressure was held constant at 1350 bar. Various optical methods were used to characterize the non-combusting and combusting sprays.

Analysis of spray-wall interaction is a major issue in the study of the combustion process in DI diesel engines. Along with spray characteristics, the investigation of impinging sprays and of liquid wall film development is fundamental for predicting the mixture formation. Simulations of these phenomena for diesel sprays need to be validated and improved; nevertheless they can extend and complement experimental measurements. In this paper the wall film thickness for impinging sprays was investigated by evaluating the heat transfer across a temperature controlled wall. In fact, heat transfer is significantly affected by the wall film thickness, and both experiments and simulations were carried out to correlate the wall temperature variations and film height. The numerical simulations were carried out using the STAR-CD and the KIVA-3V, rel. 2, codes.

The effects of multiple injections on engine-out emissions from a high-speed direct injection (HSDI) diesel engine were investigated in a series of experiments using a single cylinder research engine. Injection sequences in which the main injection was split into two, three and four pulses were tested and the resulting emissions (NOx, CO HC and particulate matter), torque and cylinder pressures were compared to those obtained with single injections. Together with the number of injections, the effects of varying the dwell time were also investigated. It was found that dividing the main injection into two parts lowered the engine-out particulate and CO emissions and increased fuel efficiency. However, it also resulted in increased NOx emissions.

Optical studies of combusting diesel sprays were done on three different alternative liquid fuels and compared to Swedish environmental class 1 diesel fuel (MK1). The alternative fuels were Rapeseed Oil Methyl Ester (RME), Palm Oil Methyl Ester (PME) and Fischer-Tropsch (FT) fuel. The studies were carried out in the Chalmers High Pressure High Temperature spray rig under conditions similar to those prevailing in a direct-injected diesel engine prior to injection. High speed shadowgraphs were acquired to measure the penetration of the continuous liquid phase, droplets and ligaments, and vapor penetration. Flame temperatures and relative soot concentrations were measured by emission based, line-of-sight, optical methods. A comparison between previous engine tests and spray rig experiments was conducted in order to provide a deeper explanation of the combustion phenomena in the engine tests.

Wall wetting can occur irrespective of combustion concept in diesel engines, e.g. during the compression stroke. This action has been related to engine-out emissions in different ways, and an experimental investigation of impinging diesel sprays is thus made for a standard diesel fuel and a two-component model fuel (IDEA). The experiment was performed at conditions corresponding to those found during the compression stroke in a heavy duty diesel engine. The spray characteristics of two fuels were measured using two different optical methods: a Phase Doppler Particle Analyzer (PDPA) and high-speed imaging. A temperature controlled wall equipped with rapid, coaxial thermocouples was used to record the change in surface temperature from the heat transfer of the impinging sprays.

The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole perpendicular to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that, at the inception stage, cavitation bubbles are dominantly seen in the vortices at the boundary layer shear flow and outside the separation zone. Cavitation bubbles grow intensively in the shear layer and develop into cloud-like coherent structures when viewed from the side of the nozzle. Shedding of the coherent cloud cavitation was observed. When the flow was increased further the cloud like cavitation bubbles developed into a large-scale coherent structure extending downstream of the hole. Under this condition the cavitation starts as a mainly glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric.

Non-circular holes are believed to have a potential in reducing the smoke emissions from a diesel engine by entraining more air into the spray due to the larger surface area exposed between fuel and air. The idea is based on results from investigations of gas jets, where the air entrainment for elliptical jets was increased substantially compared to circular jets. Non-circular nozzle holes were tested in a 2 liter single cylinder heavy duty diesel engine and compared with standard circular nozzle holes. The non-circular holes, which were made with aspect ratios of close to 2:1 and 4:1, have a similar flow rate as the conventional circular holes. Two different angles of the major axis orientation to the injector centerline were used. The engine tests were done at constant speed with both high and low load conditions and were repeated several times. Emissions, fuel consumption and cylinder pressure were measured and are presented together with calculated rate of heat release curves.

In a modern internal combustion engine, most of the fuel energy is dissipated as heat, mainly in the form of hot exhaust gas. A high temperature is required to allow conversion of the engine-out emissions in the catalytic system, but the temperature is usually still high downstream of the exhaust gas aftertreatment system. One way to recover some of this residual heat is to implement a Rankine cycle, which is connected to the exhaust system via a heat exchanger. The relatively low weight increase due to the additional components does not cause a significant fuel penalty, particularly for heavy-duty vehicles. The efficiency of a waste-heat recovery system such as a Rankine cycle depends on the efficiencies of the individual components and the choice of a suitable working fluid for the given boundary conditions.

Heat transfer from impinging sprays in direct injected diesel engines has been found to influence the rate of heat release and the formation of emissions. The use of multiple injections may also affect heat transfer. The objective of this work is to study heat transfer between the wall and the spray, and how the surface temperature of the wall affects spray behaviour in single and split injections. Two different diesel fuels were used in the experiments, noteworthy is that the diesel fuel had a higher radial penetration rate than the Idea fuel at evaporating conditions but not at non-evaporating conditions. The wall temperature has no measurable influence on radial penetration but does have a significant influence on the heat transfer.

The injection process plays an important role in Diesel engines in terms of future emission legislations. Higher injection pressures and multiple injection events every cycle are a reality. To be able to understand how the fuel injection process can be further improved studies are needed on how higher pressure, multiple injections and multi orifice nozzles affect the overall process. The objective of this study was to further develop a measurement technique to determine injection rates and discharge coefficient for multi orifice nozzles. The technique used is based on measuring the instantaneous force of a fuel jet for a non-stationary injection process. The technique is applicable for multi orifice nozzles at high injection pressures. Both single and multiple injections can be resolved.

An important objective in combustion engine research is to develop strategies for recovering waste heat and thereby increasing the efficiency of the propulsion system. Waste-heat recovery systems based on the Rankine cycle are the most efficient tools for recovering energy from the exhaust gas and the Exhaust Gas Recirculation (EGR) system. The properties of the working fluid and the expansion machine have significant effects on Rankine cycle efficiency. The expansion machine is particularly important because it is the interface at which recovered heat energy is ultimately converted into power. Parameters such as the pressure, temperature and mass-flow conditions in the cycle can be derived for a given waste-heat source and expressed as dimensionless numbers that can be used to determine whether displacement expanders or turbo expanders would be preferable under the circumstances considered.

Multi-species laser based imaging measurements have been carried out in a reacting Diesel spray in order to provide a detailed data base for model development and validation. In a high-pressure high-temperature spray chamber the measurements addressed the fuel vapor concentration, ignition and flame development and the soot formation. The fuel vapor distribution was measured quantitatively by Rayleigh scattering and compared to measurements by tracer laser-induced fluorescence. Soot volume fractions were observed by laser-induced incandescence. Fuel vapor and soot distributions were measured simultaneously and provide insight in the ignition and pollutant formation process. Specific digital image processing algorithms were developed to correct for beam steering and laser attenuation.

Soot particle size, particle concentration and volume fraction were measured by laser based methods in optically dense, highly turbulent combusting diesel sprays under engine-like conditions. Experiments were done in the Chalmers High Pressure, High Temperature spray rig under isobaric conditions and combusting commercial diesel fuel. Laser Induced Incandescence (LII), Elastic Scattering and Light Extinction were combined quasi-simultaneously to quantify particle characteristics spatially resolved in the middle plane of a combusting spray at two instants after the start of combustion. The influence that fuel injection pressure, gas temperature and gas pressure exert on particle size, particle concentration and volume fraction were studied. Probability density functions of particle size and two-dimensional images of particle diameter, particle concentration and volume fraction concerning instantaneous single-shot cases and average measurements are presented.

The discharge coefficient is an important functional parameter of an injector characterising the nozzle flow, in terms of cavitation and hydraulic flip, which subsequently play a crucial role in the spray formation and development. Thus it is important to have the possibility of measuring instantaneously the value of the discharge coefficient. The method proposed is based on the measurement of force developed during the impingement of the fuel jet on a normal target. In this study the method was verified experimentally and also the variation of a diesel nozzle discharge coefficient over the entire injection time was studied. The impingement results were in good agreement, when compared with the results from mass flow measurements both at high and low injection pressures. Strong variations of the discharge coefficient during the injector needle opening and closing periods were seen.

Thermodynamic power cycles have been shown to provide an excellent method for waste heat recovery (WHR) in internal combustion engines. By capturing and reusing heat that would otherwise be lost to the environment, the efficiency of engines can be increased. This study evaluates the maximum power output of different cycles used for WHR in a heavy duty Diesel engine with a focus on working fluid selection. Typically, only high temperature heat sources are evaluated for WHR in engines, whereas this study also considers the potential of WHR from the coolant. To recover the heat, four types of power cycles were evaluated: the organic Rankine cycle (ORC), transcritical Rankine cycle, trilateral flash cycle, and organic flash cycle. This paper allows for a direct comparison of these cycles by simulating all cycles using the same boundary conditions and working fluids.

A method for measuring apparent soot particle size and concentration in turbulent combusting diesel jets with elevated and inhomogeneous optical density is presented and discussed. The method is based on the combination of quasi-simultaneous Laser Induced Incandescence (LII), Elastic Scattering (ELS) and Light Extinction (LE) measurements exhibiting a high potential for spatially resolved measurements of carbonaceous particles in flames and residual gases at a given instant. The method evaluates the LII signal by calculating the laser fluence across the flame and compensating for signal trapping, allowing measurements where laser extinction between the flame borders reaches values up to 90%. The method was implemented by measuring particle size and concentration in the middle sagittal axis of optically dense, combusting diesel jets at a certain time after the start of combustion.

The effects of nozzle geometry on diesel spray characteristics were studied in a spray chamber under evaporating conditions using three single-hole nozzles, one cylindrical and two convergent, designated N1 (outlet diameter 140 μm, k-factor 0), N2 (outlet diameter 140 μm, k-factor 2) and N3 (outlet diameter 136 μm, k-factor 2). Spray experiments were performed with each nozzle at two constant gas densities (15 and 30 kg/m3) and an ambient temperature (673 K) at which evaporation occurs, with injection pressures ranging from 800 to 1600 bar. A light absorption and scattering method using visible and UV light was implemented, and shadow images of liquid and vapor phase fuel were recorded with high-speed video cameras. The cylindrical nozzle N1 yielded larger local vapor cone angles than the convergent nozzles N2 and N3 at both gas densities, and the difference became larger as the injection pressure increased.