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A prototype of a small, spark-ignition free-piston engine combined with a linear alternator was designed to produce electric power for portable usage. It has a bore size of 25 mm and maximum stroke of 22 mm. The engine was fueled with liquefied petroleum gas consisting of 98% propane. The electric power generated by the linear alternator is a function of the piston dynamics and the electric conductance. Therefore, the purpose of current research is to investigate the effects of the basic engine controlling parameters such as the equivalence ratio of the mixture and the spark timing on the piston dynamics and study the relationship with the electric power generation performance. The equivalence ratio of the mixture was varied from 1.0 to 1.72, while the spark timing was varied at 3, 4, and 5 mm away from the maximum top dead center. Operating characteristics, namely, indicated mean effective pressure, electric power output, operating frequency and piston stroke were analyzed.

Engine-out CO emission and fuel conversion efficiency were measured in a highly-dilute, low-temperature diesel combustion regime over a swirl ratio range of 1.44-7.12 and a wide range of injection timing. At fixed injection timing, an optimal swirl ratio for minimum CO emission and fuel consumption was found. At fixed swirl ratio, CO emission and fuel consumption generally decreased as injection timing was advanced. Moreover, a sudden decrease in CO emission was observed at early injection timings. Multi-dimensional numerical simulations, pressure-based measurements of ignition delay and apparent heat release, estimates of peak flame temperature, imaging of natural combustion luminosity and spray/wall interactions, and Laser Doppler Velocimeter (LDV) measurements of in-cylinder turbulence levels are employed to clarify the sources of the observed behavior.

The effect of the composition of propane (C₃H₈) and butane (C₄H₁₀) in liquefied petroleum gas (LPG) was investigated in a dual-fuel HCCI engine fueled with di-methyl ether (DME) and LPG. The composition of LPG affects DME-LPG dual fuel HCCI combustion due to the difference in the physical properties of propane that and butane such as octane number, auto-ignition temperature and heat of vaporization. DME was injected directly into the cylinder at various injection timing from 160 to 350 crank angle degrees (CAD). LPG was injected at the intake port with a fixed injection timing at 20 CAD. It was found that power output was increased with propane ratio. This gain in power output resulted from increased expansion work due to the better anti-knock properties of propane. However, higher propane ratio made combustion efficiency decrease because of the suppression in low temperature reaction of DME which determines heat release amount of high temperature reaction.

Dimethyl ether (DME) as a high cetane number fuel and liquefied petroleum gas (LPG) as a high octane number fuel were supplied together to evaluate the controllability of combustion phase and improvement of power and exhaust emission in homogeneous charge compression ignition (HCCI) engine. Each fuel was injected at the intake port and in the cylinder separately during the same cycle, i.e., DME in the cylinder and LPG at the intake port, or vice versa. Direct injection timing was varied from 200 to 340 crank angle degree (CAD) while port injection timing was fixed at 20 CAD. In general, the experimental results showed that DME direct injection with LPG port injection was the better way to increase the IMEP and reduce emissions. The direct injection timing of high cetane number fuel was important to control the auto-ignition timing because the auto-ignition was occurred at proper area, where the air and high cetane number fuel were well mixed.

In marine or stationary engines, consistent engine performance must be guaranteed for long-haul operations. A dual-fuel combustion strategy was used to reduce the emissions of particulates and nitrogen oxides in marine engines. However, in this case, the combustion stability was highly affected by environmental factors. To ensure consistent engine performance, the in-cylinder pressure measured by piezoelectric pressure sensors is generally measured to analyze combustion characteristics. However, the vulnerability to thermal drift and breakage of sensors leads to additional maintenance costs. Therefore, an indirect measurement via a reconstruction model of the in-cylinder pressure from engine block vibrations was developed. The in-cylinder pressure variation is directly related to the block vibration; however, numerous noise sources exist (such as, valve impact, piston slap, and air flowage).

The combustion, knock characteristics and exhaust emissions in an engine were investigated under homogeneous charge compression ignition operation fueled with liquefied petroleum gas with regard to variable valve timing and the addition of di-methyl ether. Liquefied petroleum gas was injected at an intake port as the main fuel in a liquid phase using a liquefied injection system, while a small amount of di-methyl ether was also injected directly into the cylinder during the intake stroke as an ignition promoter. Different intake valve timings and fuel injection amount were tested in order to identify their effects on exhaust emissions, combustion and knock characteristics. The optimal intake valve open timing for the maximum indicated mean effective pressure was retarded as the λTOTAL was decreased. The start of combustion was affected by the intake valve open timing and the mixture strength (λTOTAL) due to the volumetric efficiency and latent heat of vaporization.

Spray and combustion of gasoline and diesel were visualized under different ambient conditions in terms of pressure, temperature and density in a constant volume chamber. Three different ambient conditions were selected to simulate the three combustion regimes of homogeneous charge compression ignition, premixed charge compression ignition and conventional combustion. Ambient density was varied from 3.74 to 23.39 kg/m3. Ambient temperature at the spray injection were controlled to the range from 474 to 925 K. Intake oxygen concentration was also modulated from 15 % to 21 % in order to investigate the effects of intake oxygen concentrations on combustion characteristics. The injection pressure of gasoline and diesel were modulated from 50 to 150 MPa to analyze the effect of injection pressure on the spray development and combustion characteristics. Liquid penetration length and vapor penetration length were measured based on the methods of Mie-scattering and Schileren, respectively.

An experimental study was performed to evaluate the effects of ethanol blending on to gasoline spray and combustion characteristics in a spray-guided direct-injection spark-ignition engine under lean stratified operation. The spray characteristics, including local homogeneity and phase distribution, were investigated by the planar laser-induced fluorescence and the planar Mie scattering method in a constant volume chamber. Therefore, the single cylinder engine was operated with pure gasoline, 85 %vol, 50 %vol and 25vol % ethanol blended with gasoline (E85, E50, E25) to investigate the combustion and exhaust emission characteristics. Ethanol was identified to have the potential of generating a more appropriate spray for internal combustion due to a higher vapor pressure at high temperature conditions. The planar laser-induced fluorescence image demonstrated that ethanol spray has a faster diffusion velocity and an enhanced local homogeneity.

Submodels are developed for injection, evaporation and wall impingement of a liquid LPG spray. The injection model determines the quality of fuel as two-phase choke flow at the nozzle exit. Wind tunnel experiments show the spray penetration more sensitive to ambient flow velocity than to injection pressure. Most evaporation occurs during choking, while heat transfer from surrounding air has a negligible effect on downstream droplet sizes. Three dimensional simulation shows that the bathtub cavity is better than the dog-dish cavity for stable flame propagation in lean-burn conditions. The injection timing during the IVC period has a negligible effect, while injection during an intake stroke enhances fuel/air mixing to result in more homogeneous cylinder charge.

One of the major problems limiting the accuracy of piezoelectric transducers for cylinder pressure measurements in an internal-combustion (IC) engine is the thermal shock. Thermal shock is generated from the temperature variation during the cycle. This temperature variation results in contraction and expansion of the diaphragm and consequently changes the force acting on the quartz in the pressure transducer. An empirical equation for compensation of the thermal shock error was derived from consideration of the diaphragm thermal deformation and actual pressure data. The deformation and the resulting pressure difference due to thermal shock are mainly a function of the change in surface temperature and the equation includes two model constants. In order to calibrate these two constants, the pressure inside the cylinder of a diesel engine was measured simultaneously using two types of pressure transducers, in addition to instantaneous wall temperature measurement.

Lean stratified combustion shows high potential to reduce fuel consumption because it operates without the intervention of a throttle valve. Despite its high fuel economy potential, it emits large amounts of particulate matter (PM) because the locally rich mixture is formed at the periphery of a spark plug. Furthermore, the combustion phasing angle is not realized at MBT ignition timing, which can bring high work conversion efficiency. Since PM emission and work conversion efficiency are in a trade-off relation, this research focused on reducing PM emission through achieving high work conversion efficiency. Two intake air control strategies were examined in this research; throttle operation and late intake valve closing (LIVC). The experiment was conducted in a single cylinder spray-guided direct injection spark ignition (SG-DISI) engine with liquefied petroleum gas (LPG). The injected fuel amount was fixed so as to investigate the effect of each strategy.

Combustion and emission characteristics were investigated in a compression ignition engine with dual-fuel strategy using dimethyl ether (DME) and gasoline. Experiments were performed at the low load condition corresponding to indicated mean effective pressure of 0.45 MPa. DME was directly injected into the cylinder and gasoline was injected into the intake manifold during the intake stroke. The proportion of DME in the total input energy was adjusted from 10% to 100%. DME DME injection timing was widely varied to investigate the effect of injection timing on the combustion phase. Injection pressure of DME was varied from 20 MPa to 60 MPa. Exhaust gas recirculation (EGR) was controlled from 0% to 60% to explore the effect of EGR on the combustion and emission characteristics. As DME proportion was decreased with the increased portion of gasoline, the combustion efficiency was decreased but thermal efficiency was increased.

Fuel atomization and air-fuel mixing processes play a dominant role on engine performance and emission characteristics in a direct injection compression ignition engine. Understanding of microscopic spray characteristics is essential to predict combustion phenomena. The present work investigated near nozzle flow and atomization characteristics of biodiesel fuels in a constant volume chamber. Waste cooking oil, Jatropha, and Karanja biodiesels were applied and the results were compared with those of conventional diesel fuel. The tested fuels were injected by a solenoid injector with a common-rail injection system. A high-speed camera with a long distance microscopic lens was utilized to capture the near nozzle flow. Meanwhile, Sauter mean diameter (SMD) was measured by a phase Doppler particle analyzer to compare atomization characteristics.

To meet the target of the CO2 regulations, it is mandatory to replace high-carbon fossil fuels with low-carbon fuels. Diesel/Natural Gas (NG) reactivity-controlled compression ignition (RCCI) can reduce CO2 emission, which stratifies two types of fuels with different reactivity. And also, RCCI produces less NOx and particulate matter emissions by reducing the in-cylinder temperature. However, RCCI must still be enhanced in terms of the thermal and combustion efficiencies at low and medium loads. In this work, a modified piston geometry was applied to improve the RCCI combustion. The piston geometry was designed to minimize heat loss and reduce flame quenching in an RCCI engine. Experiments were conducted using a single-cylinder engine with a displacement volume of 1,000 cc. Diesel was directly injected into the cylinder, and NG was fed through the intake port.

The combustion and exhaust emission characteristics of a DME fueled HCCI engine were investigated. Different fuel injection strategies were tested under various injection quantities and timings with exhaust gas recirculation (EGR). The combustion phase in HCCI was changed by an in-cylinder direct injection and EGR, due to changes in the in-cylinder temperature and mixture homogeneity. The gross indicated mean effective pressure (IMEPgross) increased and the hydrocarbon (HC) and carbon monoxide (CO) emissions decreased as the equivalence ratio was augmented. The IMEPgross with direct injection was greater than with the port injection due to retarded ignition timing resulting from latent heat of direct injected DME fuel. It was because that most of burn duration was completed before top dead center owing to higher ignitability for DME with high cetane number. However, HC and CO emissions were similar for both injection locations.

The concentrations of individual exhaust hydrocarbon species were measured as a function of air-fuel ratio and EGR in a 2-liter four-cylinder engine using a gas chromatography, for natural gas and LPG. NMHC in addition to the species of HC, other emissions such as CO2, CO and NOx were at 1800rpm for two compression ratios (8.6 and 10.6) and various EGR ratios up to 7%. Fuel conversion efficiencies were also investigated together with emissions to study the effect of engine parameters on the combustion performances in gas engines especially under the lean burn conditions. It was found that CO2 emission decreased leaner mixture strength, the higher compression ratio and certainly with smaller C value of fuel. HC emissions from LPG engine consisted primarily of propane (larger 60%), ethylene and propylene, while main emissions from natural gas were methane (larger than 60%), ethane, ethylene and propane on the average.

The More precise control of the multiple-injection is required in common-rail injection system of direct injection diesel engine to meet the low NOx emission and optimal PM filter system. The main parameter for obtaining the multiple-injections is the mechanism controlling the injector needle energizing and movement. In this study, a piezo-driven diesel injector, as a new method driven by piezoelectric energy, has been applied with a purpose to develop the analysis model of the piezo actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code and to evaluate the effect of this control capability on spray formation processes. Aimed at simulating the hydraulic behavior of the piezo-driven injector, the circuit model has been developed and verified by comparison with the experimental results.

Influence of the inter-ring crevice, the volume between the top and second piston rings, on unburned hydrocarbon (UHC) emission was experimentally and numerically investigated. The ultimate goal of this study was to estimate the level of UHC emission induced by the blow-up of inter-ring mixture, i.e., unburned gases trapped in the inter-ring crevice. In the experiments, the inter-ring mixture was extracted to the crankcase during the late period of expansion and the early period of exhaust stroke through the engraved grooves on the lower part of cylinder wall. Extraction of the mixture resulted in the significant reductions of UHC emission in proportion to the increments of blowby flow rate, without any losses in efficiency and power. This experimental study has confirmed the importance of inter-ring crevice on UHC emission in an SI engine and established a relationship between the inter-ring mixture and UHC emission.

To investigate the mixture distributions in an LPG engine with Liquid phase port injection for heavy duty vehicles, an optical single cylinder engine, which is optically accessible both in side and bottom view, and laser diagnostic system were incorporated to apply PLIF (planar laser induced fluorescence) technique. Acetone was used as a dopant in LPG fuel, which was excited by KrF excimer laser (248nm), and its fluorescence images were acquired with ICCD camera. The effects of fuel injection timing, swirl intensity and excess air ratio were investigated. For the case of open valve injection, favorable stratification of fuel, both in axial and radial direction, was clearly observed compared to the closed valve injection, where reverse stratification in axial direction was observed. At the Ricardo swirl ratio of 3.4, it was apparent that excessive axial stratification of fuel got dominant, which would lead to poor engine performances.

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean burn operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean burn performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using a UV intensified high-speed CCD camera. Concepts of flame area speed, in addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics.