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In this paper, experimental investigation on spray atomization and droplet dynamics inside a thermostatic expansion valve (TXV), a component commonly used in vehicle refrigeration system, was conducted. A needle and an orifice were copied from a commercial TXV and machined to be mounted inside a chamber with optical access so that the flow inside the TXV is simulated and visualized at the same time. The break-up and atomization of the refrigerant were documented near the downstream of the orifice under different feed conditions for two TXV with different geometry. A Phase Doppler Anemometry (PDA) system was used later to measure the size and velocity of atomized refrigerant droplets. The results showed that the droplet size variation along the radial direction is slightly decreased at near downstream and increased at farther downstream due to the coalescence.

With the development of advanced ABE fermentation technology, the volumetric percentage of acetone, butanol and ethanol in the bio-solvents can be precisely controlled. To seek for an optimized volumetric ratio for ABE-diesel blends, the previous work in our team has experimentally investigated and analyzed the combustion features of ABE-diesel blends with different volumetric ratio (A: B: E: 6:3:1; 3:6:1; 0:10:0, vol. %) in a constant volume chamber. It was found that an increased amount of acetone would lead to a significant advancement of combustion phasing whereas butanol would compensate the advancing effect. Both spray dynamic and chemistry reaction dynamic are of great importance in explaining the unique combustion characteristic of ABE-diesel blend. In this study, a semi-detailed chemical mechanism is constructed and used to model ABE-diesel spray combustion in a constant volume chamber.

Fuel lean combustion and exhaust gas dilution are known to increase the thermal efficiency and reduce NOx emissions. In this study, experiments are performed to understand the effect of equivalence ratio on flame kernel formation and flame propagation around the spark plug for different low turbulent velocities. A series of experiments are carried out for propane-air mixtures to simulate engine-like conditions. For these experiments, equivalence ratios of 0.7 and 0.9 are tested with 20 percent mass-based exhaust gas recirculation (EGR). Turbulence is generated by a shrouded fan design in the vicinity of J-spark plug. A closed loop feedback control system is used for the fan to generate a consistent flow field. The flow profile is characterized by using Particle Image Velocimetry (PIV) technique. High-speed Schlieren visualization is used for the spark formation and flame propagation.

Hydrogen fuel is a future energy to solve the problems of energy crisis and environmental pollution. Hydrogen internal combustion engines can combine the advantage of hydrogen without carbon pollution and the main basic structure of the traditional engines. However, the power of the port fuel injection hydrogen engines is smaller than the same volume gasoline engine because the hydrogen occupies the volume of the cylinder and reduces the air mass flow. The turbocharger can increase the power of hydrogen engines but also increase the NOx emission. Hence, a comprehensive controlling strategy to solve the contradiction of the power, BTE and NOx emission is important to improve the performance of hydrogen engines. This paper shows the controlling strategy for a four-stroke, 2.3L hydrogen engine with a turbocharger. The controlling strategy divides the operating conditions of the hydrogen engine into six parts according to the engine speeds and loads.

The modeling of fuel jet atomization is key in the characterization of Internal Combustion (IC) engines, and 3D Computational Fluid Dynamics (CFD) is a recognized tool to provide insights for design and control purposes. Multi-hole injectors with counter-bored nozzle are the standard for Gasoline Direct Injection (GDI) applications and the Spray-G injector from the Engine Combustion Network (ECN) is considered the reference for numerical studies, thanks to the availability of extensive experimental data. In this work, the behavior of the Spray-G injector is simulated in a constant volume chamber, ranging from sub-cooled (nominal G) to flashing conditions (G2), validating the models on Diffused Back Illumination and Phase Doppler Anemometry data collected in vaporizing inert conditions.

Recently, with the increasing interest on some potential alternative substitutes of petroleum fuels such as biodiesel and butanol, more and more researches are focused on the field of bio-fuels because they are renewable and friendly to the environment and can possibly reduce domestic demand on foreign petroleum. Bio-fuels are generally used in the commercial market by mixing with petroleum-based diesel or gasoline. Since the volatilities and boiling points of ethanol/butanol and diesel/biodiesel fuels are significantly different, micro-explosion can be expected in the blend mixture. In this study, a numerical model of micro-explosion including bubble generation, bubble expansion, and final breakup for multi-component bio-fuel droplets is proposed. From the simulated results of droplet characteristics at the onset of micro-explosion, it is concluded that micro-explosion is possible under engine operation condition for ethanol/butanol-diesel/biodiesel fuel blends.

The combustion and emission characteristics of a diesel engine running on butanol-diesel blends were investigated in this study. The blending ratio of n-butanol to diesel was varied from 0 to 40 vol% using an increment of 10 vol%, and each blend was tested on a 2.7 L V6 common rail direction injection diesel engine equipped with an EGR system. The test was carried out under two engine loads at a constant engine speed, using various combinations of EGR ratios and injection timings. Test results indicate that n-butanol addition to engine fuel is able to substantially decrease soot emission from raw exhaust gas, while the change in NOx emissions varies depending on the n-butanol content and engine operating conditions. Increasing EGR ratio and retarding injection timing are effective approaches to reduce NOx emissions from combustion of n-butanol-diesel blends.

This paper focuses on the spray and atomization characteristics of a Dual-Fuel Injector (DFI) which includes a primary and a secondary fuel inlet. Three injectors were analyzed in this study. Apart from the DFI, two conventional diesel injectors were tested as baselines for comparison - a piezo-electric and a solenoid injector. The rail pressures ranged from 200 - 500 bar for the conventional injectors. The DFI was tested first as a single-fuel injector (by sealing the secondary inlet) at pressures ranging from 100 - 300 bar, and then in its dual-fuel mode with the primary inlet pressure ranging from 100 - 300 bar, and the secondary inlet at 25 bar higher than the primary pressure. Injection duration of 0.5 ms was chosen for the experiment. High-speed Mie scattering images were recorded to capture the spray evolution. Phase Doppler Anemometry (PDA) measurements were conducted at different locations in the spray for the acquisition of droplet sizes and velocity distributions.

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine equipped with a Bosch common rail injection system was used to study effects of injection pressures on the in-cylinder spray and combustion processes. An injector with an injection angle of 70 degrees and European low sulfur diesel fuel (cetane number 54) were used in the work. The operating load was 2.0 bar IMEP with no EGR added in the intake. The in-cylinder pressure was measured and the heat release rate was calculated. High-speed Mie-scattering technique was employed to visualize the liquid distribution and evolution. High-speed combustion video was also captured for all the studied cases using the same frame rate. NOx emissions were measured in the exhaust pipe. The experimental results indicated that for all of the conditions the heat release rate was dominated by a premixed combustion pattern. Two-stage low temperature reaction was seen for early injection timings.

Optimization of engine startup from crank to catalyst light-off is essential for achieving low emissions. For Spark Ignition Direct Injected (SIDI) engines, this requires optimization of the piston crown features, spray characteristics and control strategy. In this case study, high speed endoscope imaging was used to provide a qualitative confirmation of CFD spray predictions and to provide insight into engine starting in a “real” engine environment. The effect of piston feature was initially evaluated in a single cylinder engine running the dual-injection catalyst heating mode. The piston features were also assessed at part load and wide open throttle. The videos of the spray development were compared to CFD predictions. In the example case reported here, endoscope imaging showed that the baseline piston bowl was not effective in deflecting the spray toward the spark plug. Moving the piston bowl toward the injector gave a visible improvement in the spray deflection.

A single nozzle port fuel injector was modified to apply electrostatic charge to the fuel stream, with the intention of studying electrostatically assisted sprays in a practical, port-injected engine. The modifications were kept external to the injector and involved placing an electrode and insulating liner over the tip of the injector. The performance of the modified injector, which combined pressure driven and electrostatic atomization, was characterized in three phases: the injector sprays themselves were studied, combustion of charged fuel droplets was studied, and the injector was installed and tested on a single cylinder spark ignition engine. In the first phase, Fraunhofer diffraction measurements of droplet size, and particle image velocimetry measurements of droplet velocity were performed. The charge transferred by the sprays was measured using an electrometer, and typical forces exerted on droplets in the sprays were estimated.

This paper presents a numerical study on air-fuel mixing in a two-stroke direct injection spark ignition engine under homogeneous operation. The simulated engine is loop scavenged and uses an outwardly opening swirl injector. A generic mesh-snapping algorithm is developed to enable the moving piston to snap through transfer ports with complicated geometry. A spray model based on Linear Instability Sheet Atomization is used to describe the primary breakup of fuel sprays, and the initial rotational velocity of the conical sheet is determined from a CFD simulation of the nozzle internal flow. A wall film model accounting for the effect of contacting area is also developed to avoid the severe grid-dependence of the original film model in KIVA. Comparisons between simulations and experiments were made for sprays in quiescent ambient conditions, and a good agreement of the spray characteristics was obtained. The simulations were performed for four different injection timings.

This paper presents a study on multi-dimensional CFD modeling of scavenging and plugging in a twin-cylinder two-stroke engine. A general-purpose CFD code, KIVA, was extended to track an arbitrary number of moving pistons. The code was also modified to allow piston snapping through complicated transfer ports. Thus, a multi-cylinder simulation together with a full exhaust manifold to fully account for the interaction between scavenging and plugging becomes possible. The developed code is intended to be a numerical tool for exhaust-manifold design and optimization. The studied engine is a five-port loop scavenged twin-cylinder engine with a cylinder displacement of 432 cc. The computed exhaust pressure was compared with measured data, and reasonably good agreement was obtained. The results were also compared with those from a one-dimensional gas dynamics model, which over-predicts the plugging intensity while under-predicting the pressure loss in the exhaust manifold.

This paper describes important aspects of the development process for meeting CARB's “Ultra-Low” 3-Star emissions with engines using the new E-TEC™ direct injection system. In-house research and analysis of data from other state-of the-art engines were used to determine achievable emission levels and to set the development targets. A detailed mode-point-specific analysis of the emissions potential of the FICHT® direct injection system revealed excellent system capability in homogeneous operation and limited potential for stratified operation. Based on these results, the development work was focused on the reduction of stratified hydrocarbon emissions. Wall impingement of the fuel spray onto the piston surface was identified as a major source of hydrocarbon emissions during stratified operation. A zero-dimensional simulation of various parameters affecting wall impingement indicates that droplet size, in-cylinder temperature, and penetration velocity are the three major factors.

HCCI/PCCI combustion concepts have been demonstrated for both high brake thermal efficiency and low engine-out emissions. However, these advanced combustion concepts still could not be fully utilized partially due to the limitations of conventional fixed spray angle nozzle designs for issues related to wall wetting for early injections. The micro-variable circular orifice (MVCO) fuel injector provides variable spray angles, variable orifice areas, and variable spray patterns. The MVCO provides optimized spray patterns to minimize combustion chamber surface-wetting, oil dilution and emissions. Designed with a concise structure, MVCO can significantly extend the operation maps of high efficiency early HCCI/PCCI combustion, and enable optimization of a dual-mode HCCI/PCCI and Accelerated Diffusion Combustion (ADC) over full engine operating maps. The MVCO variable spray pattern characteristics are analyzed with high speed photographing.

In this work, an efficient and unified combustion model is introduced to simulate the flame propagation, diffusion-controlled combustion, and chemically-driven ignition in both SI and CI engine operation. The unified model is constructed upon a G-equation model which addresses the premixed flame propagation. The concept of the Livengood-Wu integral is used with tabulated ignition delay data to account for the chemical kinetics which is responsible for the spontaneous ignition of fuel-air mixture. A set of rigorously defined operations are used to couple the evolution of the G scalar field and the Livengood-Wu integral. The diffusion-controlled combustion is simulated equivalent to applying the Burke-Schumann limit. The combined model is tested in the simulation of the premixed SI combustion in a constant volume chamber, as well as the CI combustion in a conventional small bore diesel engine.

Dual-fuel combustion combining a premixed charge of compressed natural gas (CNG) and a pilot injection of diesel fuel offer the potential to reduce diesel fuel consumption and drastically reduce soot emissions. In this study, dual-fuel combustion using methane ignited with a pilot injection of No. 2 diesel fuel, was studied in a single cylinder diesel engine with optical access. Experiments were performed at a CNG substitution rate of 70% CNG (based on energy) over a wide range of equivalence ratios of the premixed charge, as well as different diesel injection strategies (single and double injection). A color high-speed camera was used in order to identify and distinguish between lean-premixed methane combustion and diffusion combustion in dual-fuel combustion. The effect of multiple diesel injections is also investigated optically as a means to enhance flame propagation towards the center of the combustion chamber.

A new approach of NOx reduction in the compression-ignition engine is introduced in this work. The previous research has shown that during the combustion stage, the high temperature ignition tends to occur early at the near-stoichiometric region where the combustion temperature is high and majority of NOx is formed; Therefore, it is desirable to burn the leaner region first and then the near-stoichiometric region, which inhibits the temperature rise of the near-stoichiometric region and consequently suppresses the formation of NOx. Such inverted ignition sequence requires mixture with inverted phi-sensitivity. Fuel selection is performed based on the criteria of strong ignition T-sensitivity, negligible negative temperature coefficient (NTC) behavior, and large heat of vaporization (HoV).

Methanol has been regarded as a potential transportation fuel due to its advanced combustion characteristics and flexible source. However, it is suffering from misfire and high HC emissions problems under cold start and low load conditions either on methanol SI engine or on methanol/diesel dual fuel engine. Hydrogen is a potential addition that can enhance the combustion of methanol due to its high flammability and combustion stability. In the current work, the effect of hydrogen fraction on the laminar flame characteristics of methanol- hydrogen-air mixture under varied equivalence ratio was investigated on a constant volume combustion chamber system coupled with a schlieren setup. Experiments were performed over a wide range of equivalence ratio of the premixed charge, varied from 0.8 to 1.4, as well as different hydrogen fraction, 0%, 5%, 10%, 15% and 20% (n/n). All tests were carried out at fixed temperature and pressure of 400K and 0.1MPa.

CNG-diesel dual fuel combustion mode has been regarded as a practical operation strategy because it not only can remain high thermal efficiency but also make full use of an alternative fuel, natural gas. However, it is suffering from misfire and high HC emissions under cold start and low load conditions. As known, hydrogen has high flammability. Thus, a certain proportion of hydrogen can be added in the natural gas (named HCNG) to improve combustion performance. In this work, the effect of hydrogen volume ratio on combustion characteristics was investigated on an optically accessible single-cylinder CNG-diesel engine using a Phantom v7.3 color camera. HCNG was compressed into the tank under different hydrogen volume ratios varied from 0% to 30%, while the energy substitution rate of` HCNG remained at 70%.