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This study investigated neat n-butanol combustion, emissions and thermal efficiency characteristics in a compression ignition (CI) engine by using two fuelling techniques - port fuel injection (PFI) and direct injection (DI). Diesel fuel was used in this research for reference. The engine tests were conducted on a single-cylinder four-stroke DI diesel engine with a compression ratio of 18.2 : 1. An n-Butanol PFI system was installed to study the combustion characteristics of Homogeneous Charge Compression Ignition (HCCI). A common-rail fuel injection system was used to conduct the DI tests with n-butanol and diesel. 90 MPa injection pressure was used for the DI tests. The engine was run at 1500 rpm. The intake boost pressure, engine load, exhaust gas recirculation (EGR) ratio, and DI timing were independently controlled to investigate the engine performance.

The use of low temperature combustion (LTC) in diesel engines tends to suppress the NOx and dry soot emissions from diesel engines. However, due to the limitations of conventional diesel fuel properties, such as the high reactivity and low volatility, implementation of LTC is highly dependent on the application of exhaust gas recirculation (EGR). While the replacement of some of the fresh air intake with the burnt exhaust gas using EGR prevents premature combustion, it also results in a reduction in thermal efficiency. In this work, the use of two different alcohol fuels, ethanol and butanol, in a high compression ratio diesel engine has been investigated to examine their potential as substitutes for conventional diesel fuel when operating under low temperature combustion mode. The effect of diesel injection timing, alcohol fuel ratios, and EGR on engine emissions and efficiency were studied at indicated mean effective pressures in the range 0.8 to 1.2 MPa.

Experimental testing was done with a modern compression ignition engine to study the effect of the engine load and the effect of different fuels on the post injection characteristics. Two different fuels were utilized; ultra-low sulphur diesel and n-butanol. The results showed that a post injection can be an effective method for increasing the operating range of the engine load. Engine operation at high load can be limited by the peak cylinder pressure but the test results showed that an early post injection can increase the engine load without increasing the peak in-cylinder pressure. Neat butanol combustion may have a very high peak in-cylinder pressure and a very high peak pressure rise rate even at low load conditions. The test results showed that a butanol post injection can contribute to engine power without significantly affecting the peak pressure rise rate and the peak in-cylinder pressure.

This study investigates neat n-butanol, as a cleaner power source, to directly replace conventional diesel fuels for enabling low temperature combustion on a modern common-rail diesel engine. Engine tests are performed at medium engine loads (6∼8 bar IMEP) with the single-shot injection strategy for both n-butanol and diesel fuels. As indicated by the experimental results, the combustion of neat n-butanol offers comparable engine efficiency to that of diesel while producing substantially lower NOx emissions even without the use of exhaust gas recirculation. The greater resistance to auto-ignition allows n-butanol to undergo a prolonged ignition delay for air-fuel mixing; the high volatility helps to enhance the cylinder charge homogeneity; the fuel-borne oxygen contributes to smoke reduction and, as a result, the smoke emissions of n-butanol combustion are generally at a near-zero level under the tested engine operating conditions.

The study investigated the characteristics of the combustion, the emissions and the thermal efficiency of a direct injection diesel engine fuelled with neat n-butanol. Engine tests were conducted on a single cylinder four-stroke direct injection diesel engine. The engine ran at 6.5 bar IMEP and 1500 rpm engine speed. The intake pressure was boosted to 1.0 bar (gauge), and the injection pressure was controlled at 60 or 90 MPa. The injection timing and the exhaust gas recirculation (EGR) rate were adjusted to investigate the engine performance. The effect of the engine load on the engine performance was also investigated. The test results showed that the n-butanol fuel had significantly longer ignition delay than that of diesel fuel. n-Butanol generally led to a rapid heat release pattern in a short period, which resulted in an excessively high pressure rise rate. The pressure rise rate could be moderated by retarding the injection timing and lowering the injection pressure.

Conventionally, the diesel fuel ignites spontaneously following the injection event. The combustion and injection often overlap with a very short ignition delay. Diesel engines therefore offer superior combustion stability characterized by the low cycle-to-cycle variations. However, the enforcement of the stringent emission regulations necessitates the implementation of innovative diesel combustion concepts such as the low temperature combustion (LTC) to achieve ultra-low engine-out pollutants. In stark contrast to the conventional diesel combustion, the enabling of LTC requires enhanced air fuel mixing and hence a longer ignition delay is desired. Such a decoupling of the combustion events from the fuel injection can potentially cause ignition discrepancy and ultimately lead to combustion cyclic variations.

As a renewable energy source, the ethanol fuel was employed with a diesel fuel in this study to improve the cylinder charge homogeneity for high load operations, targeting on ultra-low nitrogen oxides (NOx) and smoke emissions. A light-duty diesel engine is configured to adapt intake port fuelling of the ethanol fuel while keeping all other original engine components intact. High load experiments are performed to investigate the combustion control and low emission enabling without sacrificing the high compression ratio (18.2:1). The intake boost, exhaust gas recirculation (EGR) and injection pressure are independently controlled, and thus their effects on combustion and emission characteristics of the high load operation are investigated individually. The low temperature combustion is accomplished at high engine load (16~17 bar IMEP) with regulation compatible NOx and soot emissions.

In this work, engine tests were performed to realize EGR-enabled LTC on a single-cylinder common-rail diesel engine with three different compression ratios (17.5, 15 and 13:1). The engine performance was first investigated at 17.5:1 compression ratio to provide baseline results, against which all further testing was referenced. The intake boost and injection pressure were progressively increased to ascertain the limiting load conditions for the compression ratio. To extend the engine load range, the compression ratio was then lowered and EGR sweep tests were again carried out. The strength and homogeneity of the cylinder charge were enhanced by using intake boost up to 3 bar absolute and injection pressure up to 180 MPa. The combustion phasing was locked in a narrow crank angle window (5~10° ATDC), during all the tests.

Modern diesel engines were known for producing ultra-low levels of hydrogen and hydrocarbons. However, as emission control techniques such as exhaust gas recirculation (EGR) are implemented to meet stringent NOx standards, the resulting increase in partial-combustion products can be significant in quantity both as pollutants and sources of lost engine efficiency. In this work, a modern common-rail diesel engine was configured to investigate the EGR threshold for elevated carbon monoxide, hydrocarbon, and hydrogen emissions at fixed loads and fixed heat-release phasing. It is noted that increase in hydrocarbons, in particular light hydrocarbons (such as methane, ethylene, and acetylene) was concurrent with ultra-low NOx emissions. Hydrogen gas can be emitted in significant quantities with the application of very high EGR. Under ultra-low NOx production conditions for medium and high load conditions, the light hydrocarbon species can account for the majority of hydrocarbon emissions.

Extensive empirical work indicates that exhaust gas recirculation (EGR) is effective to lower the flame temperature and thus the oxides of nitrogen (NOx) production in-cylinder in diesel engines. Soot emissions are reduced in-cylinder by improved fuel/air mixing. As engine load increases, higher levels of intake boost and fuel injection pressure are required to suppress soot production. The high EGR and improved fuel/air mixing is then critical to enable low temperature combustion (LTC) processes. The paper explores the properties of the Fuels for Advanced Combustion Engines (FACE) Diesel, which are statistically designed to examine fuel effects, on a 0.75L single cylinder engine across the full range of load, spanning up to 15 bar IMEP. The lower cetane number (CN) of the diesel fuel improved the mixing process by prolonging the ignition delay and the mixing duration leading to substantial reduction of soot at low to medium loads, improving the trade-off between NOx and soot.

Diesel engines operating in the low-temperature combustion (LTC) mode generally tend to produce very low levels of NOx and soot. However, the implementation of LTC is challenged by the higher cycle-to-cycle variation with heavy EGR operation and the narrower operating corridors. Small variations in the intake charge dilution can significantly increase the unburnt hydrocarbon and carbon monoxide emissions as well as escalate the consecutive cyclic fluctuations of the cylinder charge. This in turn adversely affects the robustness and efficiency of the LTC operation. However, Improvements in the promptness and accuracy of combustion control as well as tightened control on the intake oxygen concentration can enhance the robustness and efficiency of the LTC operation in diesel engines. In this work, a set of field programmable gate array (FPGA) modules were coded and interlaced to suffice on-the-fly combustion event modulations on a cycle-by-cycle basis.

Diesel engines operating in the low-temperature combustion (LTC) mode generally tend to produce very low levels of NOx and soot. However, the implementation of LTC is challenged by the higher cycle-to-cycle variation with heavy EGR operation and the narrower operating corridors. The robustness and efficiency of LTC operation in diesel engines can be enhanced with improvements in the promptness and accuracy of combustion control. A set of field programmable gate array (FPGA) modules were coded and interlaced to suffice on-the-fly combustion event modulations. The cylinder pressure traces were analyzed to update the heat release rate concurrently as the combustion process proceeds prior to completing an engine cycle. Engine dynamometer tests demonstrated that such prompt heat release analysis was effective to optimize the LTC and the split combustion events for better fuel efficiency and exhaust emissions.

Low temperature combustion (LTC), though effective to reduce soot and oxides of nitrogen (NOx) simultaneously from diesel engines, operates in narrowly close to unstable regions. Adaptive control strategies are developed to expand the stable operations and to improve the fuel efficiency that was commonly compromised by LTC. Engine cycle simulations were performed to better design the combustion control models. The research platform consists of an advanced common-rail diesel engine modified for the intensified single cylinder research and a set of embedded real-time (RT) controllers, field programmable gate array (FPGA) devices, and a synchronized personal computer (PC) control and measurement system.

Simultaneous low NOx (< 0.15 g/kWh) & soot (< 0.01 g/kWh) are attainable for enhanced premixed combustion that may lead to higher levels of hydrocarbons and carbon monoxide emissions as the engine cycles move to low temperature combustion, which is a departure from the ultra low hydrocarbon and carbon monoxide emissions, typical of the high compression ratio diesel engines. As a result, the fuel efficiency of such modes of combustion is also compromised (up to 5%). In this paper, advanced strategies for fuel injection are devised on a modern 4-cylinder common rail diesel engine modified for single cylinder research. Thermal efficiency comparisons are made between the low temperature combustion and the conventional diesel cycles. The fuel injection strategies include single injection with heavy EGR, and early multi-pulse fuel injection under low or medium engine loads respectively.

Empirical results indicated that the engine emission and fuel efficiency of low-temperature combustion (LTC) cycles can be optimized by adjusting the fuel-injection scheduling in order to obtain appropriate combustion energy release or heat-release rate patterns. Based on these empirical results the heat-release characteristics were correlated with the regulated emissions such as soot, hydrocarbon and oxides of nitrogen. The transition from conventional combustion to LTC with the desired set of heat-release rate has been implemented. This transition was facilitated with the simplified heat-release characterization wherein each of the consecutive engine cycles was analyzed with a real-time controller embedded with an FPGA (field programmable gate array) device. The analyzed results served as the primary feedback control signals to adjust fuel injection scheduling. The experimental efforts included the boost/backpressure, exhaust gas recirculation, and load transients in the LTC region.

Extensive empirical work indicates that the exhaust emission and fuel efficiency of modern common-rail diesel engines characterise strong resilience to biodiesel fuels when the engines are operating in conventional high temperature combustion cycles. However, as the engine cycles approach the low temperature combustion (LTC) mode, which could be implemented by the heavy use of exhaust gas recirculation (EGR) or the homogeneous charge compression ignition (HCCI) type of combustion, the engine performance start to differ between the use of conventional and biodiesel fuels. Therefore, a set of fuel injection strategies were compared empirically under independently controlled EGR, intake boost, and exhaust backpressure in order to improve the neat biodiesel engine cycles.

Empirical work has been conducted with an EGR fuel reformer configured in a flow reversal and central fueling embedment to improve the fuel dispersion quality and the reforming energy efficiency. Comprehensive comparison analyses are made between the unidirectional flow and the periodic reversal flow embodiments of similar substrate size and properties; and between the inlet and central heating schemes. With a unidirectional EGR reformer, a large amount of supplemental heating is commonly required prior to reforming. The central-fueling and flow-reversal embedment in this study is shown to significantly reduce the supplemental heating energy. The EGR cooler loading for the two strategies is also analyzed. One-dimensional modeling analyses are conducted to evaluate the fuel delivery strategies and temperature profiles of the reformer at various reforming gas flow rates and engine-out exhaust temperatures and compositions.

The fatty acid alkyl esters derived from plants, rendered fats/oils and waste restaurant greases, commonly known as biodiesel, are renewable alternative fuels that may fulfill the demand gap caused by the depleting fossil diesel fuels. The combustion and emission characteristics of neat biodiesel fuels were investigated on a single cylinder of a 4-cylinder Ford common-rail direct injection diesel engine, which cylinder has been configured to have independent exhaust gas recirculation (EGR), boost and back pressures and exhaust gas sampling. The fatty acid methyl esters derived from Canola oil, soybean oil, tallow and yellow grease were first blended. Biodiesel engine tests were then conducted under the independent control of the fuel injection, EGR, boost and back pressure to achieve the low temperature combustion mode. Multi-pulse early-injections were employed to modulate the homogeneity history of the cylinder charge.

Previous work indicated that low temperature combustion (LTC) in diesel engines was capable of reducing nitrogen oxides and soot simultaneously, when implemented with highly premixed lean cylinder charge or by the use of high exhaust gas recirculation. However, the fuel efficiency of the low temperature combustion cycles was commonly compromised by the high levels of hydrocarbon and carbon monoxide emissions. Additionally, in cases of diesel homogeneous charge cycles, the combustion process may even occur before the piston completes the compression stroke, which may cause excessive efficiency reduction and combustion roughness. Empirical procedures were implemented to better phase and complete the combustion process. The impact of heat release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with zero-dimensional engine cycle simulations. This paper intends to identify the pathways to improve the fuel efficiency of diesel LTC cycles.

A number of cylinder-pressure derived parameters including the crank angles of maximum pressure, maximum rate of pressure rise, and 50% heat released are considered as among the desired feedback for cycle-by-cycle adaptive control of diesel combustion. For real-time computation of these parameters, the heat release analyses based on the first law of thermodynamics are used. This paper intends to identify the operating regions where the simplified heat release approach provides sufficient accuracy for control applications and also highlights those regions where its use can lead to significant errors in the calculated parameters. The effects of the cylinder charge-to-wall heat transfer and the temperature dependence of the specific heat ratio on the model performance are reported. A new computationally efficient algorithm for estimating the crank angle of 50% heat released with adequate accuracy is proposed for computation in real-time.