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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). A deep neural network (DNN) model is among the most feasible ways to reconstruct the in-cylinder pressure from engine block vibrations, minimizing the effect of noise or uncertainties. Vibration and in-cylinder pressure signals were measured on a natural gas (NG)/diesel dual-fuel engine using an accelerometer and a piezoelectric sensor. A parametric study was conducted to investigate the effects of the composition of the training conditions on the accuracy of the model. The main parameters, engine load, engine speed, diesel injection timing, and intake air pressure, were varied to investigate their effect on the model prediction. The results showed that the prediction accuracy was directly related to the amount of training data that had similar trends of in-cylinder pressure with the test conditions, irrespective of the total amount and types of engine parameters of the training data. With these investigations, we can identify the relationships between the training dataset and model performance that can be used in the development of a cylinder pressure reconstruction model for the real-time verification of performance in dual-fuel engines.

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. Two different engine loads were selected to represent the low and medium loads for the operation of the engine, i.e., 4.3 bar indicated mean effective pressure (IMEP) and 7.5 bar IMEP, respectively. According to the experimental results, the combustion efficiency and thermal efficiency of the modified piston were improved by up to 0.8% and 1.0%, respectively. Energy balance analysis showed that the heat transfer loss decreased by 1.1% owing to the minimal surface area of the piston. Therefore, the thermal efficiency improved. In addition, the combustion efficiency was improved because a large squish height and a small squish distance enabled the flame to reach the crevice area, which had poor conditions for flame maintenance. Heat-loss management using an modified piston geometry can contribute to the reduction in CO2 emissions in RCCI engines.

Hydrogen can be used as a fuel for internal combustion engines to realize a carbon-neutral transport society. By extending the lean limit of spark ignition engines, their efficiency, and emission characteristics can be improved. In this study, stratified charge combustion (SCC) using monofueled hydrogen direct injection was used to extend the lean limit of a spark ignition engine. The injection and ignition timing were varied to examine their effect on the SCC characteristics. An engine experiment was performed in a spray-guided single-cylinder research engine, and the nitrogen oxide and particulate emissions were measured. Depending on the injection timing, two different types of combustion were characterized: mild and hard combustion. The advancement and retardation of the ignition timing resulted in a high and low combustion stability, respectively. The lubricant-based particulate emission was attributed to the in-cylinder temperature and area of the flame surface. Therefore, the results of the study suggest that the optimization of the hydrogen SCC based on the injection and ignition timing could contribute to a clean and efficient transport sector.

Low-temperature combustion has the potential to reduce nitrogen oxides (NOx) and particulate matter (PM) emissions; however, it faces the challenge of high level of hydrocarbon (HC) and carbon mono...

The effects of turbocharger (T/C) rotational inertia on engine and turbine performance under transient and steady engine conditions were analyzed in a 2.0 L 4-cylinder turbocharged-gasoline direct injection (T-GDI) engine. The test T/Cs consisted of heavy and light compressor wheels (C/W) and turbine wheels (T/W). The study was conducted in two research stages. First, transient engine load tests were conducted to evaluate the effect of T/C rotational inertia on transient response of the T/C, combustion performance, and fuel consumption. Seconds, steady engine load tests were conducted to find out if a light inertia T/C can run at higher efficiency under the same exhaust pulsating flow conditions within one engine cycle. In order to evaluate the engine on-board turbine instantaneous performances in the units of crank angle degree (CAD), T/C rotation speed and pressure data were measured in the experiment. The instantaneous exhaust gas mass flow rate and the temperature of upstream and downstream of the turbine were extracted by 1-D simulation. Turbine efficiency and mass flow rate parameters were calculated by combining these data. In the results, there existed positive effects of light inertia T/C on response and specific fuel consumption under transient conditions. It was also found that the light inertia T/C could show higher T/C speed fluctuation under the same exhaust pulsating flow conditions. Consequently, blade speed ratio (BSR) and turbine efficiency of light inertia T/C were partially higher than that of conventional one. However, it was not led to higher engine efficiency.

Hydrogen as a fuel is feasible for future sustainable mobility. Because hydrogen has a low volumetric energy density, high-pressure hydrogen is required for high-speed fuel injection. The objective of this research is analysis of the hydrogen spray behavior depending on the ambient pressure. A high-pressure (10 MPa) hydrogen spray is visualized in a constant volume combustion chamber in which the ambient pressure and injection duration are varied. The schlieren method is utilized to capture the hydrogen spray with a high-speed camera. The characteristics of the hydrogen hollow-cone spray are investigated using high-speed spray images. High ambient pressure decreases the vertical extent of the spray penetration and its area. The centroid of the spray is contracted toward the axis of the injector until the ambient pressure reaches 2.0 MPa, and the pressure difference between the inner and outer sections of the spray is larger for high ambient pressures. At high ambient pressure, the heterogeneity of the hydrogen mixture increases. Owing to the aerodynamic effect, the contracted spray reconstructs the main hydrogen plume at the center of the injector. Moreover, hydrogen travels toward the top of the injector because of the generation of a vortex at the inner side of the spray. Based on the findings, hydrogen direct injection can contribute to sustainable mobility in the future.

The energy paradigm is shifting toward carbon-free and low-emission alternative fuels. Among the many candidates, hydrogen is considered a promising option thanks to its favorable fuel properties, including zero carbon content, high gravimetric energy density, and fast flame speed, despite its technical fuel production and storage challenges. Direct injection technology has been identified as the best approach for applying hydrogen in combustion engines to overcome the accompanying issues, such as backfire and low energy density. However, studies have yet to be conducted on hydrogen jet behavior in direct injection systems, specifically, studies that elucidate engine design and injection parameter optimization in the combustion system. Therefore, we aimed to assess hydrogen jet behavior through experiments and computational approaches comprehensively. Hydrogen was injected at 10 MPa using the direct injection method into a constant volume chamber under a quasi-steady ambient condition. Z-type high-speed Schlieren imaging was performed using a high-speed camera to visualize the hydrogen jet structure, which depicted the hydrogen jet’s vapor intermittency and vortex structure. We also performed a computational fluid dynamics (CFD) simulation to understand the aerodynamics of the jet. The results showed the formation of vortical flow in the inner core region, where the pressure was comparatively lower than that on the outer side of the jet. Our further investigation of the injection strategy showed that multiple injections were more beneficial in forming a favorable hydrogen-air mixture near the spark plug than a single injection case.

In this paper, the numerical simulation of the diesel and gasoline fuels injection in a constant volume chamber and in a cylinder under the operating conditions of a compression ignition (CI) engine is conducted. The simulation results are compared with the experimental data which derived from fast imaging techniques. In order to check out the possibility of using gasoline instead of diesel to increase the volumetric efficiency of the CI engine, the spray characteristics of the gasoline and diesel with injection pressures of 40 and 80 MPa, as well as temperatures of 243, 273 and 313 K, under cold start condition is investigated. The results show that under the same conditions, the vapor penetration length for the two fuels is approximately equal and due to the lower volatility of the diesel fuel, its liquid penetration length in 40 and 80 MPa injection pressures was found to be 7 and 9 mm higher than gasoline, respectively. In addition, the reduction in fuel temperature from 313 K to 243 K leads an increase in the penetration of gasoline and diesel liquids by 12 and 10 mm, respectively. Finally, the decrease in the evaporation rate causes a non-homogeneous mixture and results an increase in the unburned hydrocarbons and emissions.

This study investigates the influence of biodiesels on combustion and emission characteristics in a common-rail equipped small-bore single-cylinder diesel engine. The engine experiments were performed using waste-cooking-oil (WCO), Jatropha-oil, and Karanja-oil derived biodiesels. Conventional diesel was utilized as a baseline fuel. The test engine was operated at a speed of 1200 rpm and an indicated mean effective pressure of 0.5 MPa. The fuels were injected at fuel injection pressures (FIPs) of 40, 80, and 120 MPa. At the same time, the fuel injection timing was varied from −15 crank angle degrees (CAD) after top dead center (aTDC) to −3 CAD aTDC. Experimental results showed that ignition delay was directly correlated to the cetane number and had more significant effect at higher FIPs. The peak of in-cylinder pressure increased as the injection timing was advanced, due to longer ignition delay. Biodiesels showed relatively lower or equal level of nitrogen oxides (NOx) emissions compared to conventional diesel. This was mainly due to lower combustion efficiency showing high amount of smoke, HC, and CO emissions from incomplete combustion. However, for the WCO biodiesel, smoke, HC, and CO emissions could be significantly improved than other biodiesel thanks to better atomization and air-fuel mixing process.

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion can achieve low nitrogen oxides (NOX) and particulate matter (PM) emissions for wide ranges of engine operations. However, the deterioration in thermal efficiency, and hydrocarbon (HC) and carbon monoxide (CO) emissions at low loads were recognized as the barriers for expanding the low-load operating range. In this study, the causes of the barriers were investigated and a mixture preparation strategy was suggested for overcoming the barriers in a natural gas (NG)-diesel DF-PCCI engine. Combustion and energy balance analysis was conducted to evaluate the strategy. Baseline DF-PCCI was determined by combinations of diesel start of injection (SOI) and NG substitution ratio (SR) at low loads from 0.3 to 0.6 MPa indicated mean effective pressure (IMEP). An increase in the homogeneity of a fuel-air mixture in the baseline DF-PCCI effectively reduced the NOX and PM emissions but increased the HC and CO emissions in each low-load operation. As the engine load was decreased, the formation of an overly-lean mixture intensified the effects of the mixture homogeneity. Therefore, the thermal efficiency, and HC and CO emissions deteriorated at 0.3 MPa IMEP. A mixture stratification strategy was established to increase the local equivalence ratio and reactivity of the fuel-air mixture. The strategy was realized by a retarded diesel SOI, a lower NG SR, and a higher exhaust gas recirculation rate. The strategy increased the degree of constant volume combustion by enhancing the combustion performance. The enhanced combustion reduced the combustion loss, and thus, improved the thermal efficiency. The HC and CO emissions also decreased mainly due to the improved combustion and the reduced mass flow rates of the NG.

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions. Keywords: Dual fuel, Reactivity controlled compression ignition, Premixed charge compression ignition, Natural gas, Injection strategy, Exhaust gas recirculation

The effects of turbocharger rotation inertia on instantaneous turbine efficiency were analyzed in a 2.0 L four-cylinder twin-scroll turbocharged gasoline direct injection (T-GDI) engine. Two turbochargers of different weights were prepared for comparison purposes: base T/C and light T/C. In order to evaluate the instantaneous efficiency of each turbocharger, a combination of engine tests and a 1D simulation was conducted. In the experiments, the instantaneous exhaust gas pressures, upstream and downstream of the turbine, were measured. The instantaneous turbocharger rotation speed was also measured. The instantaneous temperature and mass flow rate of the exhaust gas were taken from the 1D simulation results. Through a combination of measuring and simulating exhaust gas states for the turbines, the instantaneous turbine blade speed ratio (BSR), total-to-static turbine efficiency (ηts), reduced mass flow rate (φ), and reduced turbine speed (Nred) were calculated. The light T/C showed higher fluctuations in the instantaneous turbine rotation speed compared to the base T/C. This greater response from the light T/C is due to experiencing less inertia loss, this leads to higher fluctuations in the instantaneous Nred, BSR, ηts, and φ. As a result, the light T/C shows higher turbine efficiency at certain points after the start of the exhaust gas pulse cycle. This is because the greater response of the light T/C lead the operating conditions of the turbine to more efficient regions in the turbine map.

Engine experiments were performed for measurement of regulated, unregulated, and particulate emissions using a 2.2 L transportation compression ignition engine fueled with blends of diesel and biodiesels derived from Jatropha and waste cooking oils. JB20 (20% v/v Jatropha biodiesel blended with 80% v/v diesel), WCOB20 (20% v/v waste cooking oil biodiesel blended with 80% v/v diesel), and baseline mineral diesel were used as test fuels in this study. Experiments were performed at an engine speed of 2000 rpm at five engine loads (0%, 25%, 50%, 75%, and 100% rated load). Regulated emission results exhibited that JB20 and WCOB20 emitted higher hydrocarbons and carbon monoxide (CO) at low engine loads compared to baseline diesel, whereas WCOB20 exhibited relatively higher oxides of nitrogen (NOx) emissions compared to baseline diesel. Unregulated emissions were higher at low engine loads and decreased with increasing engine load. Biodiesel blends showed relatively higher methane and ethylene trace emissions compared to baseline diesel, whereas WCOB20 showed higher formaldehyde, formic acid, iso-pentane, sulfur dioxide, and n-octane emissions compared to diesel at no load. Particulate number concentrations were relatively higher from biodiesel blends compared to baseline diesel at most engine operating conditions.

This study aims to assess the microscopic characteristics of Jatropha, Karanja, and Waste cooking oil-based biodiesels vis-a-vis conventional diesel under different ambient conditions in order to understand the in-cylinder processes, while using biodiesels produced from different feedstocks in the compression ignition engines. All test-fuels were injected in ambient atmosphere using a common-rail direct injection (CRDI) fuel injection system at a fuel injection pressure (FIP) of 40 MPa. Microscopic spray characteristics were measured using phase Doppler interferometer (PDI) in the axial direction of the spray at a distance of 60–90 mm downstream of the nozzle and at 0 to 3-mm distance from the central axis in the radial direction. All biodiesels exhibited relatively larger Sauter mean diameter (SMD) of the spray droplets and higher droplet velocities compared to baseline mineral diesel, possibly due to relatively higher fuel viscosity and surface tension of biodiesels. It was also observed that SMD of the spray droplets decreased with increasing distance in the radial and axial directions and the same trend was observed for all test-fuels.

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been demonstrated as a promising solution for simultaneous reduction of nitrogen oxides (NOX) and particulate matter (PM) emissions in heavy-duty compression ignition engines. The use of natural gas (NG) as the low-reactivity fuel in DF-PCCI combustion can expand the limited range of high load operations owing to the lower reactivity of NG than that of gasoline. However, the lower reactivity of NG results in significant hydrocarbon (HC) and carbon monoxide (CO) emissions at the low load operations. In this study, the mixture formations with and without exhaust gas recirculation (EGR) in NG-diesel DF-PCCI combustion were assessed to reduce the HC and CO emissions as well as to improve the fuel economy at low load operations. Diesel injection timing and NG substitution ratio (SR), which is defined as the proportion of energy stored in NG with respect to the total energy amount, were changed to examine the effects of the mixture formation on the DF-PCCI combustion. The NG SR, which was required to maintain the combustion phasing at a constant crank angle degree (CAD), was increased as the diesel injection timing was retarded in the mixture formation without EGR. The introduction of EGR, in addition to the diesel injection timing and the NG SR, contributed to the favorable mixture formation for the low load operations. The NOX and PM emissions were lower than the EURO VI limitations in both the mixture formations with and without EGR. When the EGR rate of 50% was applied, the indicated thermal efficiency (ITE) increased compared to the case without EGR. The increased ITE was due to the improved combustion efficiency, the higher peak heat release rate (HRR), and the shorter combustion duration. The HC and CO emissions also decreased significantly with the EGR.

In the present study, comparison of performance, combustion and emission characteristics of a single cylinder compression ignition (CI) genset engine fueled by biodiesels derived from Waste cooking oil (WCO), Jatropha and Karanja oils vis-a-vis baseline mineral diesel has been carried out. Performance and combustion investigations were carried out at constant engine speed (1500 rpm) and six engine loads (0–100%). WCO biodiesel showed slightly higher heat release rate (HRR) than baseline mineral diesel, while it was slightly lower for Karanja and Jatropha biodiesels. Hydrocarbons (HC) and oxides of nitrogen (NOX) emissions were lower, while carbon monoxide (CO) emission was relatively higher for biodiesels compared to baseline diesel. Smoke opacity was higher for Karanja and Jatropha biodiesels compared to baseline diesel. WCO biodiesel exhibited comparable smoke opacity with baseline mineral diesel except at full load, where it was relatively lower. Particulates were collected from the engine exhaust on a quartz filter paper using a partial flow dilution tunnel at 50 and 100% engine loads, for trace metal analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that trace metals such as Ca, Cu, Fe, K, Mg, Na, Zn and Al showed higher concentrations in particulates from all test fuels, while Ba, Cd, Cr, Mn and Mo showed relatively lower concentrations in the particulates collected.

Single fueled advanced combustion technologies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and low temperature diesel combustion (LTC), could make it possible to escape nitrogen oxides (NOx) and particulate matter (PM) generation. However, single fueled advanced combustion technologies have several challenges to overcome in order to be commercialized, such as combustion phase control, low combustion stability, narrow operating ranges, high level of maximum pressure rise rate (MPRR), and high amounts of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. Dual-fuel premixed charge compression ignition (DF-PCCI) combustion concepts have suggested many solutions to overcome the drawbacks of single-fueled advanced combustion technologies, such as combustion phase control, combustion stability, and limited operating range. However, high amounts of unburned HC and CO emissions are still regarded as the main hurdles of DF-PCCI combustion. In this study, the effects of global equivalence ratio ( ϕ global ) and initial charge temperature, which were controlled by means of intake throttling, charge heating, and exhaust gas recirculation (EGR) strategies, were investigated to overcome the bulk quenching phenomenon under low load conditions of DF-PCCI operation in a heavy-duty (HD) single cylinder engine. The optimized intake charge strategy which used the throttle and hot-EGR, showed the possibility of simultaneous HC and CO reduction, combustion efficiency ( η c ) improvement, and combustion stability enhancement while satisfying NOx and PM emissions under EU-VI regulations. The results suggest that controlling the charge air quantity and charge temperature is an effective way to mitigate the bulk quenching phenomenon under low load conditions on DF-PCCI.

To mitigate carbon emissions from the transportation sector, the application of hydrogen as a fuel for internal combustion engines was investigated. Owing to the merits of employing hydrogen in lean-burn spark-ignition engines, hydrogen stratified charge combustion (SCC) was tested in a constant-volume chamber. The mixture formation time (MFT) and ambient density were modulated to analyze their effects on the hydrogen SCC. Additionally, optical diagnostics were conducted to understand the behavior of the hydrogen flame. Short and long MFTs resulted in high and low burning velocities, respectively, based on the degree of fuel stratification. When the ambient density was high, nonlinear combustion characteristics were detected owing to the collapsed structure of the hydrogen jet. The measurement of a red-colored visible emission from the hydrogen SCC could be evidence of a hydrogen-rich combustion area. The local equivalence ratio and morphology of the hydrogen jet were the key parameters for the hydrogen SCC. By understanding the effects of MFT and ambient density on hydrogen SCC, high-efficient and clean transportation may be achievable with optimized injection and ignition timings.

In this study, the spray and combustion phenomena of biodiesels were investigated in a constant volume combustion chamber (CVCC). Mineral diesel was used as a baseline fuel and biodiesels derived from waste cooking oil, Karanja oil, and Jatropha oil were utilized to investigate the effect of fuel properties on spray and combustion processes. Experiments were performed at high temperature and pressure conditions in order to simulate the atmospheric environment of a diesel engines. Test fuels were injected at an injection pressure of 80 MPa using a common-rail equipped solenoid injector. Macroscopic evaporation characteristics were analyzed by high-speed shadowgraphy technique under evaporating conditions. The representative droplet size distribution and Sauter mean diameter (SMD) were measured using the Phase Doppler Interferometry (PDI) technique, which was applied to study the spray atomization characteristics of the fuels. The air-fuel equivalence ratio in the spray was calculated using mathematical correlations. The quantitative estimations of soot generation in the spray flames were compared using Hue number analysis. From the shadowgraphy images, the biodiesels showed slower air-fuel mixing characteristics than the baseline diesel due to their inferior volatility. While diesel evaporated abruptly after the fuel injection, the biodiesels showed dense liquid regions in the center of the spray plume. Biodiesels also exhibited larger SMD than the baseline mineral diesel in the fuel spray because of their higher density, viscosity, and surface tension. Despite having poor spray atomization characteristics, the calculated equivalence ratio of biodiesels was lower than that of the baseline diesel. This trend was attributed to the oxygen content of biodiesel. The flame luminosity and visible spray flame duration of biodiesels were lower than those of diesel, while the biodiesel spray flames exhibited lower sooting tendency than the baseline diesel.

An experimental study was carried out to investigate the effect of microwave-assisted plasma ignition on the combustion and emission characteristics in a 500 cm 3 single cylinder direct injection gasoline engine. The microwave-assisted plasma ignition system consisted of a 2.45 GHz magnetron (3 kW), a waveguide, a mixer and a non-resistor spark plug. The first experiments were performed in a 1400 cm 3 constant volume combustion chamber (CVCC) to clarify the mechanism of combustion enhancement by microwave ejection. The combustion tests were performed using an acetylene-air mixture at a range of relative air/fuel ratios (λ) under initial ambient pressures of 0.3 MPa and 0.5 MPa. The microwave-assisted plasma ignition has more advanced combustion phase than the conventional spark ignition showing larger initial flame kernel size and faster flame speed. The imaging results of the hydroxyl (OH) radical in ignition and flame demonstrated the potential of a faster chemical reaction by applying microwave on combustion. The microwave-assisted plasma ignition had a higher spark intensity and larger covering area than the conventional spark plug. The distribution and intensity of OH radicals on the surface of the flame were also higher with microwave ejection. In terms of engine test, lean limit was extended up to lambda 1.55 and the fuel efficiency was improved by 6% by microwave-assisted plasma ignition. The combustion phase was advanced so the peak of in-cylinder pressure and heat release rate increased more than those of conventional spark ignition. Based on the faster combustion, the combustion stability was enhanced so the lean limit was extended to lambda of 1.57. The microwave-assisted plasma ignition system was advantageous in the reduction of carbon monoxide and unburned hydrocarbon emissions, whereas nitrogen oxide emissions increased due to the higher temperatures in the combustion chamber. The engine test results finally demonstrated that the certain level of microwave ejection energy could improve all of engine performance and emission characteristics than conventional spark ignition system.

Three visualization methods, Schlieren, Shadowgraph, and Mie-scattering, were applied to compare diesel and gasoline spray structures in a constant volume chamber. Fuels were injected into a high pressure/high temperature chamber under the same in-cylinder pressure and temperature conditions of low load in a GDCI (gasoline direct injection compression ignition) engine. Two injection pressures (40 MPa and 80 MPa), two ambient pressures (4.2 MPa and 1.7 MPa), and two ambient temperatures (908 K and 677 K) were use. The images from the different methods were overlapped to show liquid and vapor phases more clearly. Vapor developments of the two fuels were similar; however, different liquid developments were seen. At the same injection pressure and ambient temperature, gasoline liquid propagated more quickly and disappeared more rapidly than diesel liquid phase. At the low ambient temperature and pressure condition, gasoline and diesel sprays with higher injection pressures showed longer liquid lengths due to higher spray momentum. At the higher ambient temperature condition, the gasoline liquid length was shorter for the higher injection pressure. Higher volatility of gasoline is the main reason for this shorter liquid length under higher injection pressure and higher ambient temperature conditions. For a design of GDCI engine, it is necessary to understand the higher volatility of gasoline.

Gasoline compression ignition (GCI), or gasoline direct-injection compression ignition (GDCI), is a concept that utilizing gasoline instead of conventional diesel fuel in a compression ignition (CI) engine for higher efficiency and lower emissions. Even though the single-injection GCI engine works well under the low load condition of 0.45 MPa indicated mean effective pressure (IMEP). In this study, the double-injection strategies including pilot- and main-injections were applied on a GCI engine under the low load condition to reduce the combustion noise. The effects of the pilot-injection timing and the pilot-injection quantity on a double-injection GCI engine with a fixed main-injection timing were investigated and compared with the single-injection GCI in a single-cylinder heavy-duty CI engine under the low load condition. In addition, the direct imaging of the flame propagation of gasoline double-injection was conducted in an optically accessible engine that was modified from the same engine to infer the emission trends. First of all, the double-injection GCI showed a reduction of the maximum pressure rise rate from 1.3 MPa/degree to 0.2 ∼ 0.3 MPa/degrees. In addition, the reduction of nitrogen-oxide (NOx) levels in half was measured compared with the single-injection GCI due to the lower combustion temperature. However, the double-injection GCI operated with nearly 5% coefficient of variation (COV) in IMEP under the most experimental conditions. IMEP and fuel economy were slightly decreased. A significant increase of the carbon monoxide (CO) and soot emissions were also shown, although the emission levels were much less than that from the conventional diesel CI engine. The flame images demonstrated that the gasoline main-injection showed a diesel-like luminous diffusion flame, which would be a main source of the soot formation, because the pilot-injection give rises to a high temperature and high pressure conditions in which gasoline from the main-injection can be ignited with shorter ignition delays.

This work investigates how morphology and nano-structure of the soot particles produced in a diesel spray flame evolve due to the rise in the temperature/pressure caused by the piston motion. The soot particles were sampled from the exhaust line of a diesel engine and were compared to the soot particles directly sampled from the spray flame of the same injector, in a constant volume chamber. Analysis of the high resolution transmission electron microscope (HRTEM) images acquired from the soot samples at two axial locations in the spray flame shows that the soot aggregates grow in size, become longer, more fractal and attain lower surface to volume ratio along the spray axis. However, the soot particles produced in the spray flame become smaller, shorter, less fractal, more compact and attain higher surface to volume ratio when emitted from the engine. This is discussed to be due to the increase in the oxidation rate by temperature rise caused by piston motion, and the consequent oxidation induced fragmentation of the soot aggregates. The effect of oxidation is also evident on the size of the soot primary particles, as the engine-out soot is found to have smaller primary particles compared to the soot initially produced in the spray flame. Nano-structural analysis shows that the crystallite size in the engine-out soot is increased compared to the soot originally produced in the spray flame. This suggests that among two possible effects of temperature on diesel soot crystallite size, being crystallite size increase due to enhanced graphitization from one hand, and crystallite size reduction due to oxidation enhancement from the other hand, the former effect is dominant and the soot particles become structurally more ordered under the effect of temperature rise caused by piston motion.

The effects of the late-intake-valve-closing strategy and the different types of cam profile were observed in a single-cylinder compression ignition research engine. Experiments were carried out with two engine loads in naturally aspirated conditions. The late-intake-valve-closing strategy exhibited an improvement in the conventional trade-off between the nitrogen oxide emissions and the smoke emissions, as stated in other relevant work. However, it was found to be effective only for the premise that a sufficiently high mass of oxygen is trapped inside the cylinder, which ensured that the smoke emissions did not deteriorate with exhaust gas recirculation. This improvement in the trade-off decreased when the global air excess ratio inside the cylinder reached close to unity. The major disadvantages of the late-intake-valve-closing strategy included deterioration in the indicated mean effective pressure and the reduced mass of oxygen trapped inside the cylinder. The decrease in the indicated mean effective pressure was attributed to the reduction in the effective compression ratio followed by the reduction in the thermal efficiency in terms of the thermodynamics. The volumetric efficiency decreased owing to the backflow of the in-cylinder charge into the intake manifold. This implied that intake boosting was necessary not only to recover the efficiency to the original level but also to extend the engine load with a sufficient amount of air. The manipulation of cam profiles yielded further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions. The flow field measurements obtained using particle image velocimetry and direct imaging of the combustion of the fuel spray demonstrated that the asymmetric cam profile effectively increased the swirl ratio inside the cylinder. Further improvement in the trade-off relationship between the nitrogen oxide emissions and the smoke emissions was realized because of this increased swirl intensity, which provided a better environment for air utilization. The smoke emissions were suppressed without a significant increase in the nitrogen oxide emissions.

A series of diesel spray combustion tests was carried out in a constant volume combustion chamber (CVCC) to investigate the effect of multiple injection strategies on cold startability. The experiments were performed under a simulated low temperature cold start condition. In-chamber pressure analysis and high speed flame imaging were conducted to compare the effectiveness of each injection strategy on cold startability. Spray targeting visualization was also performed to examine the wall impingement of injected fuel. The diesel fuel was injected into the CVCC with an injection pressure of 35 MPa. Multiple injection strategies with different amounts of pilot injection quantities were applied to improve the diesel combustion under simulated cold start ambient condition. The flame imaging and in-chamber pressure results showed that the multiple injection strategy provided better cold startability than the single injection condition. According to the pilot injection quantity, the peak of the flame luminosity and in-chamber pressure were gradually increased with larger pilot injection quantity cases. The peak of the variation rate of the in-chamber pressure with a multiple injection strategy was approximately 2 times higher than that of the single injection case. In terms of spray targeting imaging, the results indicated that the fuel impingement and flow to the piston crevice volume were increased with a larger amount of pilot2 injection. Therefore, the increment of the pilot1 injection quantity rather than the pilot2 injection quantity was suggested not only to improve cold startability, but also to reduce unburned hydrocarbon emissions under a cold start condition in a real engine.

The physio-chemical characteristics of soot particles are of importance with regard to performance of diesel after-treatment systems. In this study, the soot particles generated in a single-cylinder heavy-duty diesel engine are examined in terms of nanostructure, oxidative reactivity and volatile organic fraction (VOF), using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman micro-spectroscopy, and high resolution transmission electron microscopy (HRTEM). Five different injection strategies including single injection and multiple injections with various pilot injection amounts and dwell times were tested with and without exhaust gas recirculation (EGR), while combustion phasing, engine speed, and fuel injection quantity was matched for all cases. Results indicate that for the soot produced under EGR condition, nano-structural order (indicated by crystallite size obtained from XRD and AD1/AG resulted from the Raman Analysis) can explain the soot reactivity. However, in the absence of EGR, the reactivity trend cannot be explained by the structural order. It is discussed that a possible reason can be a higher level of in-cylinder oxidation in non-EGR cases (indicated by higher level of surface functional groups) which roughens the soot surface, and enhances the oxidation by increasing the specific soot surface area. It is also found that in the absence of EGR, different injection strategies impact the soot reactivity and VOF content, which can be explained mainly through the level of charge premixed-ness and the in-cylinder soot oxidation, and the consequent effect on the soot surface roughness. Results also show that the influence of injection strategy on the soot reactivity and VOF content tends to vanish as EGR is added.

Internal combustion (IC) engines operating on fossil fuel oil provide about 25% of the world's power (about 3000 out of 13,000 million tons oil equivalent per year-see Figure 1), and in doing so, they produce about 10% of the world's greenhouse gas (GHG) emissions (Figure 2). Reducing fuel consumption and emissions has been the goal of engine researchers and manufacturers for years, as can be seen in the two decades of ground-breaking peer-reviewed articles published in this International Journal of Engine Research (IJER). Indeed, major advances have been made, making today's IC engine a technological marvel. However, recently, the reputation of IC engines has been dealt a severe blow by emission scandals that threaten the ability of this technology to make significant and further contributions to the reduction of transportation sector emissions. In response, there have been proposals to replace vehicle IC engines with electric-drives with the intended goals of further reducing fuel consumption and emissions, and to decrease vehicle GHG emissions

International audience; As the initial stage of laser ignition, the effect of laser-induced plasma on nearby gaseous flow can have a considerable effect on further flame propagation. Laser-induced plasma is generated by concentrating a laser beam into a single point using a focusing lens. This paper presents a quantitative description of the perturbation of laser-induced plasma into a gaseous flow. Single-point laser-induced plasma generates fluctuations in the surrounding gaseous flow in a very short time (less than 200 ms), and the time-resolved velocity field can be obtained by the particle image velocimetry technique. Based on the angle and velocity of the velocity fields, it is possible to explain the movement of gaseous air flow quantitatively.; 1. 서 론 레이저(유도) 점화는 집적된 레이저 빔을 이용 하여 연료를 점화하는 방법으로, 최근 강화되는 환경 규제와 연소 성능 향상의 요구가 증가되는 가운데 각종 수송 분야에서 주목을 받고 있다. 레 이저 유도 점화는 기존 스파크를 이용한 전기 점 화 방식과는 다르게 연소실 내로 돌출된 부분이 없고 광학 장치를 통해 점화를 시킴으로써 불필요 한 열손실을 줄이고 소염 가능성도 줄일 수 있다. 또한 점화 위치의 조정이나 에너지 분배에도 자유 롭기 때문에 점화 시기·시점을 최적화할 수 있게 되고 이를 통해 빠른 화염 전파와 높은 연소 효율 을 구현할 수 있게 된다. 레이저 유도 플라즈마(LIP: Laser-Induced Plasma) 는 집적된 레이저 빔이 생성한 스파크를 일컫는 말로 레이저에 의한 에너지가 짧은 시간(10ns 이 하) 동안 특정 위치에 집중되면서 고온(10 5 K 이 상) 고압(10 3 Bar 이상)의 상태를 형성하는 것을 의 미한다. 이 플라즈마에 의한 점화 과정은 다음과 같다. 1. 일부 분자의 다광자 photo-dissociation과 이어 지는 inverse bremsstrahlung process를 통해 광자를 흡수하는 전자들이 생성 2. 광자들이 다른 분자들과 충돌하면서 이온화 를 촉진하고, 이것이 electron cascade로 이어지면서 gas breakdown(스파크, 레이저 유도 플라즈마) 형성