An experimental study of fuel injection strategies in CAI gasoline engine

Combustion of gasoline in a direct injection controlled auto-ignition (CAI) single-cylinder research engine was studied. CAI operation was achieved with the use of the negative valve overlap (NVO) technique and internal exhaust gas re-circulation (EGR). Experiments were performed at single injection and split injection, where some amount of fuel was injected close to top dead centre (TDC) during NVO interval, and the second injection was applied with variable timing. Additionally, combustion at variable fuel-rail pressure was examined.Investigation showed that at fuel injection into recompressed exhaust fuel reforming took place. This process was identified via an analysis of the exhaust-fuel mixture composition after NVO interval. It was found that at single fuel injection in NVO phase, its advance determined the heat release rate and auto-ignition timing, and had a strong influence on NO_X emission. However, a delay of single injection to intake stroke resulted in deterioration of cycle-to-cycle variability. Application of split injection showed benefits of this strategy versus single injection. Examinations of different fuel mass split ratios and variable second injection timing resulted in further optimisation of mixture formation. At equal share of the fuel mass injected in the first injection during NVO and in the second injection at the beginning of compression, the lowest emission level and cyclic variability improvement were observed.     

In-Cylinder Flow and Fuel Spray Interactions in a Stratified Spray-Guided Gasoline Engine Investigated by High-Speed Laser Imaging Techniques

Spray-guided direct injection spark-ignition engines operated in stratified charge mode have a high potential for improved fuel economy. As fuel is injected late in the compression stroke mixture preparation is crucial for reliable ignition. Multiple injections per cycle have proven to increase the overall combustion stability. Nevertheless cycle-to-cycle variations (ccv) are observed whose origin is not well understood. Strong impact of in-cylinder flows and spray-induced turbulence of preceding injections upon subsequent spray development and mixture formation is one possible reason for ccv. In this work mutual interactions of in-cylinder charge motion and sprays from multiple injections were investigated. Time resolved particle image velocimetry (PIV) and Mie scattering of fuel droplets at 16 kHz was used to simultaneously measure the temporal evolution of in-cylinder flow fields and spray formation. The data revealed significant spray-induced vortices perturbing the tumble flow. Sprays from subsequent injections were disturbed and showed greatly enhanced ccv compared to the first injection. A distinct upwards fluid flow impinging the cylinder head at the injector’s location (termed funnel flow) was identified as primary origin of spray deformation for second and third injections.     

Liquid film thickness inside the high pressure swirl injectors: Real scale measurement and evaluation of analytical equations

Liquid film thickness inside two swirl injectors for direct injection (DI) gasoline engines was measured at different injection pressure conditions ranging from 2.0 to 7.0 MPa and then previous analytical and empirical equations were examined from the experimental results. Based on the evaluation, a new equation for the liquid film thickness inside the swirl injectors was introduced. A direct photography using two real scale transparent nozzles and a pulsed light source was employed to measure the liquid film thickness inside the swirl injectors. The error in the liquid film thickness measurement, generated from different refractive indices among transparent nozzle, fuel and air, was estimated and corrected based on the geometric optics. Two injectors which have different nozzle diameter and nozzle length were applied to introduce a more general empirical equation for the liquid film thickness inside the pressure swirl injectors. The results showed that the liquid film thickness remains constant at the injection pressures for direct injection gasoline engines while the ratio of nozzle length to nozzle diameter (L/D) shows significant effect on the liquid film thickness. The previously introduced analytical and empirical equations for relatively low injection pressure swirl injectors overestimated the effect of injection pressure at the operating range of high pressure swirl injectors and, in addition, the effect of L/D ratio and swirler geometry was rarely considered. A new empirical equation was suggested based on the experimental results by taking into account the effects of fuel properties, nozzle diameter, nozzle length and swirler geometry.     

Heat flux characteristics of spray wall impingement with ethanol,butanol, iso-octane,gasoline and E10 fuels

Future fuel stocks for spark-ignition engines are expected to include a significant portion of bio-derived components with quite different chemical and physical properties to those of liquid hydrocarbons. State-of-the-art high-pressure multi-hole injectors for latest design direct-injection spark-ignition engines offer some great benefits in terms of fuel atomisation, as well as flexibility in in-cylinder fuel targeting by selection of the exact number and angle of the nozzle’s holes. However, in order to maximise such benefits for future spark-ignition engines and minimise any deteriorating effects with regards to exhaust emissions, it is important to avoid liquid fuel impingement onto the cylinder walls and take into consideration various types of biofuels. This paper presents results from the use of heat flux sensors to characterise the locations and levels of liquid fuel impingement onto the engine’s liner walls when injected from a centrally located multi-hole injector with an asymmetric pattern of spray plumes. Ethanol, butanol, iso-octane, gasoline and a blend of 10% ethanol with 90% gasoline (E10) were tested and compared. The tests were performed in the cylinder of a direct-injection spark-ignition engine at static conditions (i.e. quiescent chamber at 1.0 bar) and motoring conditions (at full load with inlet plenum pressure of 1.0 bar) with different engine temperatures in order to decouple competing effects. The collected data were analysed to extract time-resolved signals, as well as mean and standard deviation levels of peak heat flux. The results were interpreted with reference to in-cylinder spray formation characteristics, as well as fuel evaporation rates obtained by modelling. In addition, high-speed images of single droplets of fuel impinging onto the array of the heat flux sensor were acquired with simultaneous sampling of the heat flux signal in an attempt to provide further interpretation. The single droplet tests showed ability of the signals to quantify droplet mass impinged on the sensor. Analysis of the peak heat flux at static engine conditions quantified values of fuel temperature at impingement in agreement with the wet bulb temperatures predicted by the droplet evaporation model. Comparison of the static and motoring engine heat flux signals around the bore showed the effect of the intake flow on the spray’s pattern at impingement and demonstrated fuel presence on the liner that survived at exhaust valve open timing. The general behaviour was different for the alcohols to that of the hydrocarbons, with ethanol exhibiting the effect of its high latent heat on the signals and butanol exhibiting effects related to poor atomization and slow evaporation.     

An experimental study of the combustion characteristics in SCCI and CAI based on direct-injection gasoline engine

Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion and stratified charge combustion at lower peak temperatures with a variable compression ratio, a variable intake temperature and a trapped rate of the EGR using NVO (negative valve overlap). This experiment was attempted to investigate the origins of these lower temperature auto-ignition phenomena with SCCI and CAI using gasoline fuel. In case of SCCI, the combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. We investigated the effects of air–fuel ratio, residual EGR rate and injection timing on the CAI combustion area. In addition, the effect of injection timing on combustion factors such as the start of combustion, its duration and its heat release rate was also investigated.     

Stereoscopic multi-planar PIV measurements of in-cylinder tumbling flow

The non-reacting flow field within the combustion chamber of a motored direct-injection spark-ignition engine with tumble intake port is measured. The three-dimensionality of the flow necessitates the measurement of all three velocity components via stereoscopic particle-image velocimetry in multiple planes. Phase-locked stereoscopic PIV is applied at 15 crank angles during the intake and compression strokes, showing the temporal evolution of the flow field. The flow fields are obtained within a set of 14 axial planes, covering nearly the complete cylinder volume. The stereoscopic PIV setup applied to engine in-cylinder flow and the arising problems and solutions are discussed in detail. The three-dimensional flow field is reconstructed and analyzed using vortex criteria. The tumble vortex is the dominant flow structure, and this vortex varies significantly regarding shape, strength, and position throughout the two strokes. The tumble vortex center moves clockwise through the combustion chamber. At first, the tumble has a c-shape which turns into an almost straight tube at the end of the compression. Small-scale structures are analyzed by the distribution of the turbulent kinetic energy. It is evident that the symmetry plane only represents the 3D flow field after 100 CAD. For earlier crank angles, both kinetic energy (KE) and turbulent kinetic energy (TKE) in the combustion chamber are well below the KE and TKE in the symmetry plane. This should be taken into account when the injection and breakup of the three-dimensional fuel jet are studied. The mean kinetic energy is conserved until late compression by the tumble motion. This conservation ensures through the excited air motion an enhancement of the initial air-fuel mixture which is of interest for direct-injection gasoline engines.     

PIV, 2D-LIF and 1D-Raman measurements of flow field,composition and temperature in premixed gas turbine flames

Several laser diagnostic measurement techniques have been applied to study the lean premixed natural gas/air flames of an industrial swirl burner. This was made possible by equipping the burner with an optical combustion chamber that was installed in the high-pressure test rig facility at the DLR Institute of Combustion Technology in Stuttgart. The burner was operated with preheated air at various operating conditions with pressures up to p = 6 bar and a maximum thermal power of P = 1 MW.The instantaneous planar flow field inside the combustor was studied with particle image velocimetry (PIV). Planar laser induced fluorescence (PLIF) of OH radicals on a single-shot basis was used to determine the shape and the location of the flame front as well as the spatial distribution of reaction products. 1D laser Raman spectroscopy was successfully applied for the measurement of the temperature and the concentration of major species under realistic gas turbine conditions.Results of the flow field analysis show the shape and the size of the main flow regimes: the inflow region, the inner and the outer recirculation zone. The highly turbulent flow field of the inner shear layer is found to be dominated by small and medium sized vortices. High RMS fluctuations of the flow velocity in the exhaust gas indicate the existence of a rotating exhaust gas swirl. From the PLIF images it is seen that the primary reactions happened in the shear layers between inflow and the recirculation zones and that the appearance of the reaction zones changed with flame parameters. The results of the multiscalar Raman measurements show a strong variation of the local mixture fraction allowing conclusions to be drawn about the premix quality. Furthermore, mixing effects of unburnt fuel and air with fully reacted combustion products are studied giving insights into the processes of the turbulence–chemistry interaction.     

Comparison of Combustion Models and Assessment of Their Applicability to the Simulation of Premixed Turbulent Combustion in IC-Engines

In order to simulate the turbulent combustion process occurring in spark-ignition (IC) engines, it is necessary to provide suitable and numerically economical models, the latter being particularly important in the application to industrial problems. Moreover, these models must deliver sufficiently accurate results for the unsteady operation of spark combustion engines, concerning variable geometries, temperatures, pressures and charge development in different configurations. In this work different turbulent combustion models for premixed hydrocarbon combustion are compared with respect to their ability to accurately predict the propagation of turbulent perfectly premixed flames. As a first configuration a cylinder of constant volume was studied. Transient calculations were used to simulate the propagation of the turbulent flame and to evaluate the resulting turbulent burning velocity. These calculations were performed for a perfect mixture of air and hydrocarbons at stoichiometric mixture and different initial conditions concerning pressure, temperature and turbulence intensity. As a second configuration a stationary turbulent bunsen-type flame with methane fuel was used to validate the turbulent combustion model of [Lindstedt and Vaos, Combust. Flame 116 (1999) 461] at different pressures. Calculated results were then compared to experimental data of [Kobayashi, Tamura, Maruta and Niioka. In: Proceedings of the 26th Symposium on Combustion, 1996, p. 389] and show excellent agreement for the turbulent burning velocity at several pressure levels using only a single set of model parameters.     

Air flow and pressure inside a pressure-swirl spray and their effects on spray development

Air flow and pressure inside a pressure-swirl spray for direct injection (DI) gasoline engines and their effects on spray development have been analyzed at different injector operating conditions. A simulation tool was utilized and the static air pressure at the centerline of the spray was measured to investigate the static pressure and flow structure inside the swirl spray. To investigate the effect of static air pressure on swirl spray development, a liquid film model was applied and the Mie-scattered images were captured. The simulation and experiment showed that recirculation vortex and air pressure drop inside the swirl spray were observable and the air pressure drop was greater at high injection pressure. At high fuel temperature, the air pressure at the nozzle exit showed higher value compared to the atmospheric pressure and then continuously decreased up to few millimeters distance from the nozzle exit. The pressure drop at high fuel temperatures was more than that of atmospheric temperature. This reduced air pressure was recovered to the atmospheric pressure at further downstream. The results from the liquid film model and macroscopic spray images showed that the air pressure started to affect the liquid film trajectory about 3 mm from the nozzle exit and this effect was sustained until the air pressure recovered to the atmospheric pressure. However, the entrained air motion and droplet size have more significant influence on the spray development after the most of the liquid sheet is broken-up and the spray loses its initial momentum.     

The Effect of Fuel-Injection Timing on In-cylinder Flow and Combustion Performance in a Spark-Ignition Direct-Injection (SIDI) Engine Using Particle Image Velocimetry (PIV)

This study applies particle image velocimetry (PIV) to an optical spark-ignition direct-injection engine in order to investigate the effects of fuel-injection on in-cylinder flow. Five injection timing combinations, each employing a stoichiometric 1:1 split ratio double-injection strategy, were analysed at an engine speed of 1200 RPM and an intake pressure of 100 kPa. Timings ranged from two injections in the intake stroke to two injections in the compression stroke, resulting in a variety of in-cylinder environments from well-mixed to highly turbulent. PIV images were acquired at a sampling frequency of 5 kHz on a selected swirl plane. The flow fields were decomposed into mean and fluctuating components via two spatial filtering approaches — one using a fixed 8 mm cut-off length, and the other using a mean flow speed scaled cut-off length which was tuned in order to match the turbulent kinetic energy (TKE) profile of a 300 Hz temporal filter. From engine performance tests, the in-cylinder pressure traces, indicated mean effective pressure (IMEP), and combustion phasing data showed very high sensitivity to injection timing variations. To explain the observed trend, correspondence between the measured flow and these performance parameters was evaluated. An expected global trend of increasing turbulence with retarded injection timing was clearly observed; however, relationships between TKE and burn rate were not as obvious as anticipated, suggesting that turbulence is not the predominant factor associated with injection timing variations which impacts engine performance. Stronger links were observed between bulk flow velocity and burn rate, particularly during the early stages of flame development. Injection timing was also found to have a significant impact on combustion stability, where it was observed that low-frequency flow fluctuation intensity revealed strong similarities with the coefficient of variance (CoV) of IMEP, suggesting that these fluctuations are a suitable measure of cycle-to-cycle variation — likely due to the influence of bulk flow on flame kernel development.     

Improved atomization,collision and sub-grid scale momentum coupling models for transient vaporizing engine sprays

A computationally efficient spray model is presented for the simulation of transient vaporizing engine sprays. It is applied to simulate high-pressure fuel injections in a constant volume chamber and in mixture preparation experiments in a light-duty internal combustion engine. The model is based on the Lagrangian-Particle/Eulerian-Fluid approach, and an improved blob injection model is used that removes numerical dependency on the injected number of computational parcels. Atomization is modeled with the hybrid Kelvin–Helmholtz/Rayleigh–Taylor scheme, in combination with a drop drag model that includes Mach number and Knudsen number effects. A computationally efficient drop collision scheme is presented, tailored for large numbers of parcels, using a deterministic collision impact definition and kd-tree data search structure to perform radius-of-influence based, grid-independent collision probability estimations. A near-nozzle sub-grid scale flow-field representation is introduced to reduce numerical grid dependency, which uses a turbulent transient gas-jet model with a Stokes–Strouhal analogy assumption. An implicit coupling method was developed for the Arbitrary Lagrangian–Eulerian (ALE) turbulent flow solver. A multi-objective genetic algorithm was used to study the interactions of the various model constants, and to provide an optimal calibration. The optimal set showed similar values of the primary breakup constants as values used in the literature. However, different values were seen for the gas-jet model constants for accurate simulations of the initial spray transient. The results show that there is a direct correlation between the predicted initial liquid-phase transient and the global gas-phase jet penetration. Model validation was also performed in engine simulations with the same set of constants. The model captured mixture preparation well in all cases, proving its suitability for simulations of transient spray injection in engines.     

Hydraulic characterization of high temperature hydrocarbon liquid jets

An experimental study has been conducted to investigate the hydraulic characteristics of a plain orifice nozzle issuing pressurized high-temperature liquid hydrocarbon, in order to simulate injection of aviation fuel after being used as coolant in an active cooling system in a hypersonic flight vehicle. The fuel was heated to 553 K (280°C) using an induction heater, at an upstream pressure of up to 1.0 MPa, and injected to atmospheric pressure conditions through a sharp-edged orifice of diameter 0.7 mm and length 4.3 mm. It has been observed that the isothermal lines on the plane of the mass flow rate versus the square root of the pressure drop (ΔP) were clearly affected by increased fuel temperatures, and the discharge coefficient (C_d) decreased sharply with increasing fuel injection temperature (T_inj) above the fuel boiling point of 460 K. The Reynolds number (Re) for three ΔPs with respect to T_inj reached maxima and then began to decrease as T_inj increased for each ΔP case, and the fuel temperature of maximum Re at a given pressure condition increased as ΔP increased. The effects of cavitation on the hydraulic characteristics of the high temperature fuel were explored by representing C_d with respect to three cavitation numbers and dissipation efficiency. The behaviors of C_d showed a clear dependency on cavitation number, and all of the results collapsed to a single curve, regardless of ΔP. In addition, the curve indicated that the C_d characteristics was divided into non-cavitating and cavitating regions by the critical cavitation numbers near the fuel boiling point, and a sharp decrease in C_d was found to be typical in the cavitating region. The relationship between C_d and Re showed that when T_inj exceeded the boiling point the high temperature liquid jets experienced a sharp decrease in C_d at a determined Reynolds number, due to the collapse of the mass flow rate induced by the choked cavitaiton.     

Experimental study of syngas combustion at engine-like conditions in a rapid compression machine

As the world energy demand and environmental concern continue to grow, syngas is expected to play an important role in future energy production. It represents a viable energy source, particularly for stationary power generation, since it allows for a wide flexibility in fossil fuel sources, and since most of the harmful contaminants and pollutants can be removed in the post-gasification process prior to combustion. In this work, two typical mixtures of H₂, CO, CH₄, CO₂ and N₂ have been considered as representative of the producer gas coming from wood gasification, and its turbulent combustion at engine-like conditions is made in a rapid compression machine in order to improve current knowledge and provide reference data for modeling and simulation of internal combustion engines. Methane as main constituent of the natural gas is used as reference fuel for comparison reasons. Single compression and compression- expansion events were performed as well direct light visualizations from chemiluminescence emission. There is an opposite behavior of the in-cylinder pressure between single compression and compression-expansion strokes. For single compression, peak pressure decreases as the ignition delay increases. In opposite, for compression-expansion the peak pressure increases as the ignition delay increases. This opposite behavior has to do with the combustion duration under constant volume conditions. Conclusion can be drawn that higher pressures are obtained with methane-air mixture in comparison to both typical syngas compositions. These results could be endorsed to the heat of reaction of the fuels, air to fuel ratio and burning velocity. Another major finding is that syngas typical compositions are characterized by high ignition timings due to its low burning velocities. This could compromise the use of typical syngas compositions on high rotation speed engines.     

Transient heating effects in high pressure Diesel injector nozzles

The tendency of today’s fuel injection systems to reach injection pressures up to 3000 bar in order to meet forthcoming emission regulations may significantly increase liquid temperatures due to friction heating; this paper identifies numerically the importance of fuel pressurization, phase-change due to cavitation, wall heat transfer and needle valve motion on the fluid heating induced in high pressure Diesel fuel injectors. These parameters affect the nozzle discharge coefficient (C_d), fuel exit temperature, cavitation volume fraction and temperature distribution within the nozzle. Variable fuel properties, being a function of the local pressure and temperature are found necessary in order to simulate accurately the effects of depressurization and heating induced by friction forces. Comparison of CFD predictions against a 0-D thermodynamic model, indicates that although the mean exit temperature increase relative to the initial fuel temperature is proportional to (1 − C_d²) at fixed needle positions, it can significantly deviate from this value when the motion of the needle valve, controlling the opening and closing of the injection process, is taken into consideration. Increasing the inlet pressure from 2000 bar, which is the pressure utilized in today’s fuel systems to 3000 bar, results to significantly increased fluid temperatures above the boiling point of the Diesel fuel components and therefore regions of potential heterogeneous fuel boiling are identified.     

High-speed imaging for direct-injection gasoline engine research and development

In recent years, new laser and camera technology have enabled the development of high-speed imaging diagnostics for measurements at frame rates commensurate with the time scales of turbulent mixing, combustion, and emission formation in internal combustion engines. The ability to study the evolution of in-cylinder flow, fuel/air mixing, ignition, and combustion within individual cycles and for many consecutive cycles provides new insights into the physics and chemistry of internal combustion engine performance. Data for model development and device development are obtained with unprecedented access to the identification of random events such as cycle to cycle variation and ignition instabilities. This paper summarizes high-speed diagnostics developments with a focus on application to spark-ignition direct-injection gasoline engines. A range of optical techniques is described along with examples of applications in research and near-production engines. Measurements of in-cylinder velocities were conducted with particle image velocimetry. The spray evolution was followed with Mie scattering. Quantitative fuel distributions were recorded with laser-induced fluorescence. Fuel impingement on surfaces was quantified with refractive index matching. Combined velocity and fuel measurements were used to study ignition reliability. Chemiluminescence techniques provided insights into the evolution of the spark plasma as well as the growing flame kernel. Chemiluminescence and black body radiation imaging yielded insights into the formation and oxidation of soot.     

Atomization and spray characteristics of bioethanol and bioethanol blended gasoline fuel injected through a direct injection gasoline injector

The focus of this study was to investigate the spray characteristics and atomization performance of gasoline fuel (G100), bioethanol fuel (E100), and bioethanol blended gasoline fuel (E85) in a direct injection gasoline injector in a gasoline engine. The overall spray and atomization characteristics such as an axial spray tip penetration, spray width, and overall SMD were measured experimentally and predicted by using KIVA-3V code.The development process and the appearance timing of the vortices in the test fuels were very similar. In addition, the numerical results accurately described the experimentally observed spray development pattern and shape, the beginning position of the vortex, and the spray breakup on the spray surface. Moreover, the increased injection pressure induced the occurrence of a clear circular shape in the downstream spray and a uniform mixture between the injected spray droplets and ambient air. The axial spray tip penetrations of the test fuels were similar, while the spray width and spray cone angle of E100 were slightly larger than the other fuels. In terms of atomization performance, the E100 fuel among the tested fuels had the largest droplet size because E100 has a high kinematic viscosity and surface tension.     

High efficiency fuel sleds for polar traverses

We describe here the evolution of lightweight, high-efficiency fuel sleds for Polar over-snow traverses. These sleds consist of flexible bladders strapped to sheets of high molecular weight polyethylene. They cost 1/6th, weigh 1/10th and triple the fuel delivered per towing tractor compared with steel sleds. An eight-tractor fleet has conducted three 3400-km roundtrips to South Pole with each traverse delivering ～320,000 kg of fuel while emitting <1% the pollutants, consuming 1/2 the fuel and saving ～$1.6 M compared with aircraft resupply. A two-tractor fleet in Greenland recently delivered ～83,000 kg of fuel in bladder sleds to Summit with similar benefits. Performance monitoring has revealed that bladder-sled towing resistance is largely governed by sliding friction, which can start high and drop in half over the first 30 min of travel. Frictional heating probably produces a thin water layer that lubricates the sled–snow interface. Consequently, towing resistance depends on the thermal budget of the sled. For example, black fuel bladders increase solar gain and thus decrease sled resistance; data suggest they could double again the fuel delivered per tractor. The outstanding efficiency and low cost of these sleds has transformed fuel delivery to Polar research stations.     

Experimental study on turbulent mixing of spray droplets in crossflow

Centrifugal spray injected at various angles in gas crossflow has been studied experimentally using PIV visualization system and image-processing techniques. Experiments were carried out inside a rectangular duct (95 mm × 95 mm in cross-section) at ambient temperature and pressure, with different gas Reynolds numbers (vary from 12,900 to 45,000) and three injection angles (60°, 90° and 120°). The spray angle of the centrifugal nozzle is 80°, with D₃₂ of 80 μm. The instantaneous images of droplets distribution and the values of the line-averaged D₃₂ at different positions on the cross-sections along the flow field for each condition were obtained, and their flow field configurations were achieved. Quantitative assessments of mixing degree between two phases for different injection angles were determined using a spatial unmixedness parameter. It is found that the addition of droplets into the gas crossflow enhanced the turbulence intensity of the gas crossflow and caused different-scale vortices. The flow field structure, to a great extent, is dependent on the injection angle. The entrainment and centrifugal force of large vortex lead to uneven droplet distribution and moreover influence the mixing of droplets and gas crossflow. A better mixing result can be obtained with the injection angle of nozzles of 60°.     

Measurements of ultrafine particles from a gas-turbine burning biofuels

Measurements of ultrafine particles have been performed at the exhaust of a low emission microturbine for power generation. This device has been fuelled with liquid fuels, including a commercial diesel oil, a mixture of the diesel oil with a biodiesel and kerosene, and tested under different loads. Primarily attention has been focused on the measurements of the size distribution functions of the particles emitted from the system by using particle differential mobility analysis. A bimodal size distribution function of the particle emitted has been found in all the examined conditions. Burning diesel oil, the first mode of the size distribution function of the combustion-formed particles is centered at around 2–3 nm, whereas the second mode is centered at about 20–30 nm. The increase of the turbine load and the addition of 50% of biodiesel has not caused changes in the shape of size distribution of the particles. A slightly decrease of the amount of particle formed has been found. By using kerosene the amount of emitted particles increases of more than one order of magnitude. Also the shape of the size distribution function changes with the first mode shifted towards larger particles of the order of 8–10 nm but with a lower emission of larger 20–30 nm particles. Overall, in this conditions, the mass concentration of particles is increased respect to the diesel oil operation. Particle sizes measured with the diesel oil have been compared with the results on a diesel engine operated in the same power conditions and with the same fuel. Measurements have showed that the mean sizes of the formed particles do not change in the two combustion systems. However, diesel engine emits a number concentration of particles more than two orders of magnitude higher in the same conditions of power and with the same fuel. By running the engine in more premixed-like conditions, the size distribution function of the particles approaches that measured by burning kerosene in the microturbine indicating that the distribution function of the sizes of the emitted particles can be strongly affected by combustion conditions.