The first stage of ignition in saturated hydrocarbon fuels (in diesel combustion) is characterized as low temperature heat release (LTHR) or cool flame combustion. LTHR takes place as a series of isomerization reactions at temperatures from 600K to 900K, and is often detectable in HCCI, rapid compression machines, and early injection low temperature combustion (LTC). The experimental investigation presented attempts to determine the existence of LTHR behavior in late injection low temperature combustion in a medium duty diesel engine with both petroleum diesel and biodiesel fuels and to determine the influence of such behavior on LTC torque and emissions. Three experiments were performed to meet these objectives: the first studies two operating modes (conventional combustion with -8° after top dead center injection timing and 0% EGR and low temperature combustion with 0° after top dead center injection timing and nominally 42% EGR level) with standard petroleum diesel, palm biodiesel, and soy biodiesel; the second studies a sweep of EGR level from 0% to nominally 45% with petroleum diesel and palm biodiesel with a constant injection timing of 0° after top dead center. The third and final experiment utilized petroleum diesel, soy biodiesel, and blends from the two fuels (20 and 50% soy biodiesel) to see the influence of viscosity and density on LTHR. LTHR is apparent in all fuels' rates of heat release profiles at the LTC operating conditions. Diesel fuel LTC displays a longer and more intense LTHR phase. Lower amounts of LTHR in the palm biodiesel causes less sensitivity to EGR, less instability, and produces better torque and emission characteristics. Density and viscosity only change the shape of the LTHR duration, while cetane number or ignition quality affects the length of the LTHR duration. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155575

Internal combustion engines have dealt with increasingly restricted emissions requirements. After-treatment devices are successful in bringing emissions into compliance, but in-cylinder combustion control can reduce their burden by reducing engine out emissions. For example, oxides of nitrogen (NOx) are diesel combustion exhaust species that are notoriously difficult to remove by after-treatment. In-cylinder conditions can be controlled for low levels of NOx, but this produces high levels of soot potentially leading to increased particulate matter (PM). The simultaneous reduction of NOx and PM can be realized through a combustion process known as low temperature combustion (LTC). In this study, the typical definition of LTC as the defeat of the inverse relationship between soot and NOx is not applicable as a return to the soot-NOx tradeoff is observed with increasing exhaust gas recirculation (EGR). It is postulated that this effect is the result of an increase in the hot ignition equivalence ratio, moving the combustion event into a slightly higher soot formation region. This is important because a simple emissions based definition of LTC is no longer helpful. In this study, the manifestation of LTC in the calculated heat release profile is investigated. The conditions classified as LTC undergo a two-stage ignition process. Two-stage ignition is characterized by an initial cool-flame reaction followed by typical hot ignition. In traditional combustion conditions, the ignition is fast enough that a cool-flame is not observed. By controlling initial conditions (pressure, temperature, and composition), the creation and duration of the cool-flame event is predictable. Further, the effect that injection timing and the exhaust gas recirculation level have on the controlling factors of the cool-flame reaction is well correlated to the duration of the cool-flame event. These two results allow the postulation that the presence of a sufficiently long cool-flame reaction indicates a combustion event that can be classified as low temperature combustion. A potential method for identifying low temperature combustion events using only the rate of heat release profile is theorized. This study employed high levels of EGR and late injection timing to realize the LTC mode of ordinary petroleum diesel fuel. Under these conditions, and based on a 90 percent reduction in nitric oxide and no increase in smoke output relative to the chosen baseline condition, a two part criteria is developed that identifies the LTC classified conditions. The criteria are as follow: the combustion event of conventional petroleum diesel fuel must show a two-stage ignition process; the first stage (cool-flame reaction) must consume at least 2 percent of the normalized fuel energy before the hot ignition commences.

Biodiesel and different biodiesel-diesel blends were run in a production compression ignition engine to determine optimized engine control module (ECM) settings for each fuel. Focus was placed on a combination of exhaust gas recirculation (EGR) ratio and start of injection (SOI) timing, as these parameters are easily modified and have significant effects on engine emissions. Tests were run at low to moderate engine load at different engine speeds. It was found that with the ECM0́9s default settings, higher blends of biodiesel tended to result in higher NOx emissions and lower soot emissions, in line with previous studies. It was also found that increasing the EGR ratio to account for the different stoichiometric air-fuel ratio of biodiesel was effective in bringing NOx emissions to similar or lower levels compared with those of petroleum diesel. At low load conditions, improved fuel economy could also be achieved by advancing the start of injection relative to the ECM default timing. Pure soybean biodiesel was also run with high rates of EGR and modified injection schemes in order to achieve simultaneous reduction of NOx and soot emissions consistent with low temperature combustion. At low load conditions, increasing the EGR ratio to high levels was sufficient to achieve very low NOx and soot emissions. As engine load increased, high levels of EGR brought NOx emissions to very low levels, but soot emissions increased substantially. The amount of EGR was increased to the point of combustion deterioration without seeing a reduction in soot emissions. Thus, the engine0́9s default injection strategy needed to be modified in order to achieve low temperature combustion. Strategies found effective were a reduced amount of pre-injection, later injection timing, and a combination of the two. With these strategies, low temperature combustion was achieved through a moderate range of engine load. To see the effect of engine speed, cases were run at different speeds with a constant load. Modifications to the injection strategy were found to be beneficial at different engine speeds.

This book examines internal combustion engine technology and applications of biodiesel fuel. It includes seven chapters in two sections. The first section examines engine downsizing, fuel spray, and economic comparison. The second section deals with applications of biodiesel fuel in compression-ignition and spark-ignition engines. The information contained herein is useful for scientists and students looking to broaden their knowledge of internal combustion engine technologies and applications of biodiesel fuel.

One of the promising solutions to rising emission standards is the in-cylinder emission reduction, through low temperature combustion. Low temperature combustion defeats conventional soot-NOx trade off by simultaneous reduction of both emissions by controlling the in-cylinder temperature below the Soot and NOx forming temperature zones. The use of low temperature combustion strategy phases the combustion into the expansion stroke, making the entire combustion process highly sensitive to start of high temperature combustion. Early start of high temperature combustion results in the advancement of combustion, resulting in higher in-cylinder temperature and pressure promoting the formation of oxides of nitrogen. Delayed start of combustion results in the retardation of the high temperature combustion further into the expansion stroke the first stage combustion, in this case cool flame combustion, has an important role to play in the phasing of high temperature combustion, associated emissions and efficiency. The focus of this study is to investigate the difference in the cool flame combustion characteristics between petroleum diesel and soybean biodiesel, when operating in low temperature combustion mode. Previous studies have attributed the absence of the cool flame in biodiesel purely due to oxygen content of the biodiesel. Cycle-to-cycle variation, exhaust gas constituents, rail pressure and fuel penetration length were analyzed to determine the causes for difference in the cool flame characteristic between the two fuels. The result of the analysis was that cool flame combustion is present in all combustion processes and not a product of systematic error or due to the combustion of the partially combusted species in the recirculated exhaust gas. It does not entirely depend on the chemical composition of fuel and rather on the in-cylinder conditions in particular the ambient oxygen concentration. Lower ambient oxygen concentration causes the cool flame to advance with respect to the high temperature heat release, making it visible in the heat release profile. The appearance of the cool flame at increased rail pressure in biodiesel does not cause a change in the trend of ignition delay, unburned hydrocarbon or carbon monoxide with respect to rail pressure. It only results in the retardation of high temperature combustion, further into the expansion stroke. Low temperature combustion defeats conventional soot-NOx trade off by simultaneous reduction of both emissions by controlling the in-cylinder temperature below the Soot and NOx forming temperature zones. In this study, low temperature combustion is achieved with the use of high exhaust gas recirculation circulation and late injection timing, phasing the combustion in the expansion stroke. The use of low temperature combustion strategy phases the combustion into the expansion stroke, making the entire combustion process highly sensitive to start of high temperature combustion. Early start of high temperature combustion results in the advancement of combustion, resulting in higher in-cylinder temperature and pressure promoting the formation of oxides of nitrogen. Delayed start of combustion results in the retardation of the high temperature combustion further into the expansion stroke, increasing the concentration of unburned hydrocarbon in the exhaust. Hence the first stage combustion, in this case cool flame combustion, has an important role to play in the phasing of high temperature combustion, associated emissions and efficiency. The focus of this study is to investigate the difference in the cool flame combustion characteristics between petroleum diesel and soybean biodiesel, when operating in low temperature combustion mode. Previous studies have attributed the absence of the cool flame in biodiesel purely due to oxygen content of the biodiesel. Late injection timing along with EGR was used to achieve LTC combustion (verified by soot-NOx comparison with conventional combustion), to realize the difference in cool flame characteristics between the two fuels. Further, cycle-to-cycle variation, exhaust gas constituents, rail pressure and fuel penetration length were analyzed to determine the causes for difference in the cool flame characteristic between the two fuels. The result of the analysis was that cool flame combustion is present in all combustion processes and not a product of systematic error or due to the combustion of the partially combusted species in the recirculated exhaust gas. It does not entirely depend on the chemical composition of fuel and rather on the in-cylinder conditions in particular the ambient oxygen concentration. Lower ambient oxygen concentration causes the cool flame to advance with respect to the high temperature heat release, making it visible in the heat release profile. The appearance of the cool flame at increased rail pressure in biodiesel does not cause a change in the trend of ignition delay, unburned hydrocarbon or carbon monoxide with respect to rail pressure. It only results in the retardation of high temperature combustion, further into the expansion stroke. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151940

Research Paper (postgraduate) from the year 2019 in the subject Engineering - Chemical Engineering, course: M.TECH, language: English, abstract: This work is an experimental study for the measurement of ignition delay characteristics of burning fuel sprays in cylindrical combustion chambers. It is carried out on hot air and high pressure. The objective of the study is to investigation the effect of hot air temperature and a well as high pressure on ignition delay of diesel fuel sprays. The effect of blending of n-Pentane with pure diesel was investigated. An experimental set up was design for this purpose with the emphasis on optical method for measurement of ignition delay at various pressures. The results presented here show that ignition delay of diesel fuel spray decreases with increase in the temperature and pressure of hot air. Results also show the effect of methyl group being more dominant at low ignition temperatures and that of alkyl group being more dominant at higher temperature. Blending of n-pentane with diesel fuel, increase its ignition delay at low ignition temperatures. However, as the concentration of blending fuel was increased beyond 30%, the ignition temperature increase. Ignition temperature for 40% pentane blends is much higher that the pure diesel.

Compression ignition engines have been used widely in the transportation sector and power generation for the decades. These engines are less fuel consumed with higher brake thermal efficiency. However, compression ignition engines produce higher pollution in NOx and PM emission as well as cause several negative drawbacks to the environment. Most countries in the world have regulated several regulations to reduce the emission from the engines. Other than that, the introduction of biodiesel in the engines is beneficial and proven to reduce the emission significantly. However, biodiesel has higher density and viscosity with lower heating value as compared to mineral diesel. Fuel additives are among other methods that proven to modify the properties of biodiesel to be comparable with mineral diesel without doing any engine modification. Although fuel additives' ability to reduce harmful emissions is well known in the literature, the mechanism for these additives is not well understood when operated in the four-stroke, four-cylinder diesel engines. Two alcohol-based additives, methanol and ethanol were diluted with B 20 blend (20% biodiesel + 80% mineral diesel) with the formulation of 5% by volume. The test fuels; mineral diesel, B100 (palm-diesel), B20 blend and B20-alcohol blends (B20 E5 and B20 M5) were investigated on a Mitsubishi 4D68 four stroke, four-cylinder water-cooled diesel engine incorporating sensors for in-cylinder pressure measurement and thermocouples. There were two operating modes dealing with these fuels, which the first mode been conducted on increasing engine speeds at 50% throttle position. While as for the second mode, these fuels were operated at three different engine loads, 0.05 MPa, 0.4 MPa and 0.7 MPa with the engine constant speed of 2500 rpm. The effect of test fuels on brake power, brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), combustion (in-cylinder pressure, rate of heat release, cylinder temperature) and NOx, NO, CO and CO2 emissions were investigated. Results found that the performance of diesel engine improved with the use of alcohol (ethanol and methanol) in the B20 blends especially in comparison to mineral diesel, B100 and B20. Overall, the results indicated that when compared to mineral diesel, B100, B20, B20 E5 and B20 M5 have higher brake thermal efficiency. The use of alcohol as a fuel additive in the B20 blend has improved the combustion characteristics when the loads were applied to the engine. Besides, the exhaust emission for the B20 E5 and B20 M5 were fairly reduced when compared to mineral diesel.