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This paper presents the latest results for a new high efficiency clean diesel combustion system – Adaptive PCCI Combustion (a premixed charge compression ignition mixed-mode combustion) using a micro-variable circular orifice (MVCO) fuel injector. Key characteristics of the new combustion system such as low NOx and soot emissions, high fuel efficiency, increased engine torque are presented through KIVA simulation results. While early premixed charge compression ignition (PCCI) combustion reduces engine-out NOx and soot, it's limited to partial loads by known issues such as combustion control, high HC and CO, and high pressure rise rate, etc. Conventional combustion is well controlled diffusion combustion but comes with high NOx and soot. Leveraging the key merits of PCCI and conventional combustion in a practical engine is both meaningful and challenging.

Laser diagnostics of fuel sprays are often hampered by multiple scattering effects. Planar laser-induced exciplex fluorescence (PLIEF) and Mie scattering images of a spray are presented, and the effects of multiple signal scattering are explored. A hollow-cone spray is cut in half with a spray cutter, and then imaged from either side. In one set, signal passes through the spray to the camera (back-cut images), and in the other set it does not (front-cut images), showing the effect of passing the signal through the spray to the camera. The cut spray is characterized with a phase Doppler anemometer (PDA) and Sauter Mean Diameter (SMD) is seen to range from 10-30 μm. Operational guidelines for using the cutter are presented. It was determined that a film forms on the cutter face 3-5 ms after the start of injection (ASOI) depending on the cutter temperature. Stripped droplets from this film increase droplet concentration and SMD in the center of the spray if the cutter is used improperly.

A numerical study of micro-explosion in multi-component droplets is presented. The homogeneous nucleation theory is used in describing the bubble generation process. A modified Rayleigh equation is then used to calculate the bubble growth rate. The breakup criterion is then determined by applying a linear stability analysis on the bubble-droplet system. After the explosion/breakup, the atomization characteristics, including Sauter mean radius and averaged velocity of the secondary droplets, are calculated from conservation equations. Micro-explosion can be enhanced by introducing biodiesel into the fuel blends of ethanol and tetradecane. Micro-explosion is more likely to occur at high ambient pressure. However, increasing the ambient temperature does not have a significant effect on micro-explosion. There exists an optimal composition in the liquid mixture for micro-explosion.

Biodiesel fuels and their blends with diesel are often used to reduce emissions from diesel engines. However, biodiesel has been shown to increase the NOx emissions. Operating a compression ignition engine in low-temperature combustion mode as well as using multiple injections can reduce NOx emissions. Experimental data for biodiesel are compared to those for diesel to show the effect of the biodiesel on the peak pressure, temperature, and emissions. Accurate prediction of biodiesel properties, combined with the KIVA 3V code, is used to investigate the combustion of biodiesel. The volume fraction of the cylinder that has temperatures greater than 2200 K is shown to directly affect the production of oxides of nitrogen. Biodiesel is shown to burn faster during the combustion events, though the ignition delay is often longer for biodiesel compared to diesel.

Low Temperature Compression Ignition (LTCI) combustion employing multiple injection strategies in an optically accessible single-cylinder small-bore High-Speed Direct-Injection (HSDI) diesel engine equipped with a Bosch common-rail electronic fuel injection system was investigated in this work. Heat release characteristics were analyzed through the measurement of in-cylinder pressure. The whole cycle combustion process was visualized with a high-speed digital video camera by imaging natural flame luminosity and three-dimensional like combustion structures were obtained by taking flame images from both the bottom of the optical piston and the side window. The transient in-cylinder late cycle soot distribution was obtained by applying a Backward Illumination Light Extinction (BILE) technique through side windows. Based on the flame luminosity and soot spatially integrated signal, new parameters were defined to evaluate the combustion performance and soot formation characteristics.

The operation of a small bore high speed direct injection (HSDI) engine with a MVCO injector is simulated by the KIVA 3V code, developed by Los Alamos National Laboratory. The MVCO injector extends the range of injection timings over conventional injectors and it extra flexibility in designing injection schemes. Combustion from very early injection is observed with MVCO injections but not with conventional injection. This improves the fuel economy of the engine in terms of lower ISFC. Even better efficiency can be achieved by using biodiesel, which may be due to extra oxygen in the fuel improving the combustion process. Biodiesel sees a longer ignition delay for the initial injection. It also exhibits a faster burning rate and shorter combustion duration. Biodiesel also lowered both NOx and soot emissions. This is consistent with the general observation for soot emissions.

The KIVA-3V code, developed by Los Alamos National Laboratory, with modifications that improve its capability with biodiesel simulations was used to model the operation of an HSDI engine using blends of soybean biodiesel and diesel. Biodiesel and their blends with diesel are frequently used to reduce emissions from diesel engines, although previous studies showed that biodiesel may increase NOx emission. The paradox may be resolved by running the engine in low temperature combustion mode with biodiesel/diesel blends, as low temperature combustion simultaneously reduced NOx and soot. The modified KIVA code predicts the major combustion characteristics: peak combustion pressure, heat release rate and ignition timing accurately when compared with experimental measurements. It also correctly predicts the trend of NOx emissions. It was observed that the cylinder temperature distribution has a strong effect on emission levels.

As engine researchers are facing the task of designing more powerful, more fuel efficient and less polluting engines, a large amount of research has been focused towards homogeneous charge compression ignition (HCCI) operation for diesel engines. Ignition timing of HCCI operation is controlled by a number of factors including intake temperatures, exhaust gas recirculation (EGR) and injection timing to name a few. This study focuses on the computational modeling of an optically accessible high-speed direct-injection (HSDI) small bore diesel engine. In order to capture the phenomena of HCCI operation, the KIVA computational code package has been outfitted with an improved and optimized Shell autoignition model, the extended Zeldovich thermal NOx model, and soot formation and oxidation models. With the above named models in place, several cases were computed and compared to experimentally measured data and captured images of the DIATA test engine.

Biodiesel fuel can be produced from a wide range of source materials that affect the properties of the fuel. The diesel engine has become a highly tuned power source that is sensitive to these properties. The objectives of this research were to measure and predict the key properties of biodiesel produced from a broad range of source materials to be used as inputs for combustion modeling; and second to compare the results of the model with and without the biodiesel fuel definition. Substantial differences in viscosity, surface tension, density and thermal conductivity were obtained relative to reference diesel fuels and among the different source materials. The combustion model revealed differences in the temperature and emissions of biodiesel when compared to reference diesel fuel.

A multicomponent fuel film vaporization model using continuous thermodynamics is developed for multidimensional spray and wall film modeling. The vaporization rate is evaluated using the turbulent boundary-layer assumption and a quasi-steady approximation. Third-order polynomials are used to model the fuel composition profiles and the temperature within the liquid phase in order to predict accurate surface properties that are important for evaluating the mass and moment vaporization rates and heat flux. By this approach, the governing equations for the film are reduced to a set of ordinary differential equations and thus offer a significant reduction in computational cost while maintaining adequate accuracy compared to solving the governing equations for the film directly.

Pure diesel and biodiesel were tested inside a constant-volume combustion chamber which simulates the in-cylinder conditions similar to a diesel engine and is more flexible to change the engine operation boundary conditions. The ambient temperature effect on flame lift-off length for both fuels was first investigated with fixed injection pressure, duration, ambient density, and ambient oxygen concentration. This was determined from time-averaged OH chemiluminescence imaging technique. Then, the impacts of the observed lift-off length variations on oxygen ratio upstream of the lift-off location and the soot formation process were also studied. A Forward Illumination Light Extinction (FILE) soot measurement technique was adopted to study the soot formation process. The FILE technique with the capability of two-dimensional time-resolved quantitative soot measurement provides the much-needed information to investigate the soot formation mechanism.

In-cylinder soot formation processes of Environmentally Controlled Diesel (ECD), Diesel #2 and Tetradecane were studied with the newly developed forward illumination light extinction (FILE) soot measurement technique. Quantitative soot measurement was achieved in the constant-volume spray chamber with the proper treatment of chamber window reflection and flame radiation when applying the FILE technique. A better understanding of the soot formation process of ECD combustion under the typical engine conditions was obtained based on FILE soot measurement and flame emission measurement. Diesel #2 with higher sulfur content demonstrates a similar combustion process as ECD but more soot is generated within combustion. In contrast, much lower soot amount was found within the flame of Tetradecane. However, during the last soot oxidation period, the differences were small for all fuels.

In this paper, a new-developed forward illumination light extinction (FILE) soot measurement technique is introduced. This technique has the capability to give two-dimensional time-resolved quantitative soot measurements. Applying the light extinction theory, the line-of-sight soot volume fraction is determined by the ratio of reflected light intensities with and without a soot cloud. The advantages of this technique include its non-intrusiveness, ease of application, requirement of only one optically accessible window, and suitability for the study of transient cycle-to-cycle variations. The application of the FILE technique for diesel combustion in a constant volume chamber demonstrates the applicability and advantages of this technique. Three stages of soot formation during diesel combustion were determined using this technique.

An optically accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system was used to study the effects of multiple injection strategies on the in-cylinder combustion processes. The operating conditions were considered typical in the metal engine under moderate load conditions. In-cylinder pressure traces are used to analyze heat release characteristics. The combustion modes transit from the Homogeneous Charge Compression Ignition (HCCI)-like combustion mode to conventional diesel combustion by changing injection parameters. The whole cycle combustion process was visualized through a high-speed digital video camera and the combustion images clearly show the combustion mode transition. Laser-Induced Exciplex Fluorescence (LIEF) technique was used to obtain simultaneous liquid and vapor fuel distributions within the combustion chamber, with tetradecane-TMPD-naphthalene as the base fuel-dopant combination.

Homogeneous Charge Compression Ignition (HCCI) combustion employing single main injection strategies in an optically accessible single cylinder small-bore High-Speed Direct Injection (HSDI) diesel engine equipped with a Bosch common-rail electronic fuel injection system was investigated in this work. In-cylinder pressure was taken to analyze the heat release process for different operating parameters. The whole cycle combustion process was visualized with a high-speed digital camera by imaging natural flame luminosity. The flame images taken from both the bottom of the optical piston and the side window were taken simultaneously using one camera to show three dimensional combustion events within the combustion chamber. The engine was operated under similar Top Dead Center (TDC) conditions to metal engines. Because the optical piston has a realistic geometry, the results presented are close to real metal engine operations.

This paper describes a numerical study on air/fuel preparation process in a direct-injected spark-ignition engine under partial load stratified conditions. The fuel is represented as a mixture of four components with a distillation curve similar to that of actual gasoline, and its vaporization processes are simulated by two recently formulated multicomponent vaporization models for droplet and film, respectively. The models include major mechanisms such as non-ideal behavior in high-pressure environments, preferential vaporization, internal circulation, surface regression, and finite diffusion in the liquid phase. A spray/wall impingement model with the effect of surface roughness is used to represent the interaction between the fuel spray and the solid wall. Computations of single droplet and film on a flat plate were first performed to study the impact of fuel representation and vaporization model on the droplet and film vaporization processes.

The blow-by phenomenon is seldom acquainted with diesel engines, but for a small bore HSDI optical diesel engine, the effects are significant. A difference in peak pressure up to 25% can be observed near top-dead-center. To account for the pressure differences, a 0-D crevice flow model with a dynamic ring pack model was incorporated into the KIVA code to determine the amount of blow-by. The ring pack model will take into account the forces acting on the piston rings, the position of the piston rings, and the pressure located at each region of the crevice volume at every time step. The crevice flow model takes into consideration the flow through the circumferential gap, ring gap, and the ring side clearance. As a result, the cylinder mass, trapped mass in the crevice regions, and the blow-by values are known. Validation of the crevice model is accomplished by comparing the in-cylinder motoring pressure trace with the experimental motoring data.

The possibility of producing butanol efficiently with the use of fermentation processes has been recently demonstrated. This could potentially lead to the production from renewable sources of a fuel that has energy density significantly increased with respect to the currently widely used ethanol. We provide preliminary experimental results on the structure of butanol electrosprays (droplet size and velocity measurements with Phase-Doppler Anemometry) with a particular emphasis on the determination of the dependence of droplet size on mass flow rate and applied electric field. In parallel, a comparison is provided with the electrosprays of low conductivity fuels for which data are available from previous published studies. These preliminary results show significant differences from low-conductivity fuel electrosprays that practically produce monodisperse aerosols, the droplet size of which can be controlled by spray flow rate.

Combustion processes employing different injection strategies in a High-Speed Direct Inject (HSDI) diesel engine were investigated using a narrow angle injector (70 degree). Whole-cycle combustion was visualized using a high-speed digital video camera. The liquid spray evolution process was imaged by the Mie-scattering technique. Different injection strategies were employed in this study including early pre-Top Dead Center (TDC) injection, post-TDC injection, multiple injection strategies with an early pre-TDC injection and a late post-TDC injection. Smokeless combustion was obtained under some operating conditions. Compared with the original injection angle (150 degree), some new combustion phenomena were observed for certain injection strategies. For early pre-TDC injection strategies, liquid fuel impingement is observed that results in some newly observed fuel film combustion flame (pool fires) following an HCCI-like weak flame.

An optically-accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system is used to study the effects of differing injection strategies on combustion and soot. Laser-Induced Incandescence (LII) is used to visualize the evolution and distribution of soot within the combustion chamber from the onset of ignition to late into the expansion stroke. A low-sooting fuel, blended from two single component fuels, is used for experimentation. Because of the low-sooting nature of the fuel blend, the lean operating conditions, and optical distortion of the complex shaped engine, acceptable LII signal levels are difficult to obtain. Therefore a low-sulfur European Diesel fuel is also employed during experimentation. Acceptable LII signal levels are obtained using the Diesel fuel, however, without extreme caution, surface damage to the optical components of the engine are possible.