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Technical Paper

A Fuel Sensitive Ignition Delay Model for Direct Injection Diesel Engine Operating under EGR Diluted Conditions

2018-04-03
2018-01-0231
This empirical work investigates the impacts of thermodynamic parameters, such as pressure and temperature, and fuel properties, such as fuel Cetane number and aromatic contents on ignition delay in diesel engines. Systematic tests are conducted on a single-cylinder research engine to evaluate the ignition delay changes due to the fuel property differences at low, medium and high engine loads under different EGR dilution ratios. The test fuels offer a range of Cetane numbers from 28 to 54.2 and aromatic contents volume ratios from 19.4% to 46.6%. The experimental results of ignition delays are used to derive an ignition delay model modified from Arrhenius’ expression. Following the same format of Arrhenius’ equation, the model incorporates the pressure and temperature effects, and further includes the impacts of intake oxygen concentration, fuel Cetane number and aromatic contents volume ratio on the ignition delay.
Technical Paper

A Simplified Circuit Model for the Emulation of Glow Phase during Spark Discharge

2018-04-03
2018-01-0092
The ever-growing demand to meet the stringent exhaust emission regulations have driven the development of modern gasoline engines towards lean combustion strategies and downsizing to achieve the reduction of exhaust emission and fuel consumption. Currently, the inductive ignition system is still the dominant ignition system applied in Spark Ignited (SI) engines. It is popular due to its simple design, low cost and robust performance. The new development in spark ignition engines demands higher spark energy to be delivered by the inductive ignition system to overcome the unfavorable ignition conditions caused by the increased and diluted in-cylinder charge. To meet this challenge, better understanding of the inductive ignition system is required. The development of a first principle model for simulation can help in understanding the working mechanism of the system in a better way.
Journal Article

An Empirical Study to Extend Engine Load in Diesel Low Temperature Combustion

2011-08-30
2011-01-1814
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.
Journal Article

An Enabling Study of Diesel Low Temperature Combustion via Adaptive Control

2009-04-20
2009-01-0730
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.
Journal Article

An Improvement on Low Temperature Combustion in Neat Biodiesel Engine Cycles

2008-06-23
2008-01-1670
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.
Technical Paper

An Investigation of Near-Spark-Plug Flow Field and Its Effect on Spark Behavior

2019-04-02
2019-01-0718
In the recent decades, the emission and fuel efficiency regulations put forth by the emission regulation agencies have become increasingly stringent and this trend is expected to continue in future. The advanced spark ignition (SI) engines can operate under lean conditions to improve efficiency and reduce emissions. Under such lean conditions, the ignition and complete combustion of the charge mixture is a challenge because of the reduced charge reactivity. Enhancement of the in-cylinder charge motion and turbulence to increase the flame velocity, and consequently reduce the combustion duration is one possible way to improve lean combustion. The role of air motion in better air-fuel mixing and increasing the flame velocity, by enhancing turbulence has been researched extensively. However, during the ignition process, the charge motion can influence the initial spark discharge, resulting flame kernel formation, and flame propagation.
Technical Paper

An Investigation on the Regeneration of Lean NOx Trap Using Ethanol and n-Butanol

2019-04-02
2019-01-0737
Reduction of nitrogen oxides (NOx) in lean burn and diesel fueled Compression Ignition (CI) engines is one of the major challenges faced by automotive manufacturers. Lean NOx Trap (LNT) and urea-based Selective Catalytic Reduction (SCR) exhaust after-treatment systems are well established technologies to reduce NOx emissions. However, each of these technologies has associated advantages and disadvantages for use over a wide range of engine operating conditions. In order to meet future ultra-low NOx emission norms, the use of both alternative fuels and advanced after-treatment technology may be required. The use of an alcohol fuel such as n-butanol or ethanol in a CI engine can reduce the engine-out NOx and soot emissions. In CI engines using LNTs for NOx reduction, the fuel such as diesel is utilized as a reductant for LNT regeneration.
Technical Paper

Clean Combustion in a Diesel Engine Using Direct Injection of Neat n-Butanol

2014-04-01
2014-01-1298
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.
Technical Paper

Combustion and Exhaust Gas Speciation Analysis of Diesel and Butanol Post Injection

2015-04-14
2015-01-0803
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.
Technical Paper

Development of a Compact Reverse-Flow Catalytic Converter for Diesel Dual Fuel LEV

1999-10-25
1999-01-3558
Upon an innovative compact design, extraordinary heat retention capability is demonstrated with a reverse-flow catalytic converter (RFC). By periodical flow reversal, the monolith solid to gas-flow thermal energy recovery, which generates a superior temperature profile oscillating along the monolith flow-path, escalates the temperature-rise by the exothermic reaction of THC and CO. Thus, the averaged temperature level of the catalytic monolith is raised substantially independent of the inflow gas temperature from engine exhaust, while an ordinary flow-through catalyst would lose light off following similar operations with low exhaust temperatures. Along the exhaust flow-path of a typical diesel-dual fuel RFC operation, the monolith center temperature is highly elevated from the boundary temperatures, while the boundary temperatures are approximating the inflow exhaust temperature.
Technical Paper

Early Pilot Injection Strategies for Reactivity Control in Diesel-ethanol Dual Fuel Combustion

2018-04-03
2018-01-0265
This paper examines the diesel-ethanol dual fuel combustion at medium engine loads on a single-cylinder research diesel engine with a compression ratio of 16.5:1. The effect of exhaust gas recirculation (EGR) and ethanol energy ratio was investigated for the dual fuel combustion to achieve simultaneously ultra-low NOx and soot emissions. A medium ethanol ratio of about 0.6 was found suitable to meet the requirements for mixing enhancement and ignition control, which resulted in the lowest NOx and soot emissions among the tested ethanol ratios. A double-pilot injection strategy was found competent to lower the pressure rise rate owing to the reduced fuel quantity in the close-to-TDC injection. The advancement of pilot injection timing tended to reduce the CO and THC emissions, which is deemed beneficial for high EGR operations. The reactivity mutual-modulation between the diesel pilot and the background ethanol mixture was identified.
Journal Article

Efficiency & Stability Improvements of Diesel Low Temperature Combustion through Tightened Intake Oxygen Control

2010-04-12
2010-01-1118
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.
Technical Paper

Empirical Study of Energy in Diesel Combustion Emissions with EGR Application

2011-08-30
2011-01-1817
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.
Technical Paper

Energy Efficiency Analysis between In-cylinder and External Supplemental Fuel Strategies

2007-04-16
2007-01-1125
Preliminary empirical and modeling analyses are conducted to evaluate the energy efficiency of in-cylinder and external fuel injection strategies and their impact on the energy required to enable diesel particulate filter (DPF) regeneration for instance. During the tests, a thermal wave that is generated from the engine propagates along the exhaust pipe to the DPF substrate. The thermal response of the exhaust system is recorded with the thermocouple arrays embedded in the exhaust system. To implement the external fuel injection, an array of thermocouples and pressure sensors in the DPF provide the necessary feedback to the control system. The external fuel injection is dynamically adjusted based on the thermal response of the DPF substrate to improve the thermal management and to reduce the supplemental energy. This research intends to quantify the effectiveness of the supplemental energy utilization on aftertreatment enabling.
Technical Paper

Energy Efficiency Comparison between Butanol and Ethanol Combustion with Diesel Ignition

2015-04-14
2015-01-0859
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.
Journal Article

Experimental Investigation of Diesel-Ethanol Premixed Pilot-Assisted Combustion (PPAC) in a High Compression Ratio Engine

2016-04-05
2016-01-0781
In this work, empirical investigations of the diesel-ethanol Premixed Pilot-Assisted Combustion (PPAC) are carried out on a high compression ratio (18.2:1) single-cylinder diesel engine. The tests focus on determining the minimum ethanol fraction for ultra-low NOx & soot emissions, effect of single-pilot vs. twin-pilot strategies on emissions and ignition controllability, reducing the EGR requirements, enabling clean combustion across the load range and achieving high efficiency full-load operation. The results show that both low NOx and almost zero soot emissions can be achieved but at the expense of higher unburned hydrocarbons. Compared to a single-pilot injection, a twin-pilot strategy reduces the soot emissions significantly and also lowers the NOx emissions, thereby reducing the requirements for EGR. The near-TDC pilot provides excellent control over the combustion phasing, further reducing the need of a higher EGR quantity for phasing control.
Technical Paper

Fuel Efficiency Improvements of Low Temperature Combustion Diesel Engines

2008-04-14
2008-01-0841
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.
Journal Article

Fuel Injection Strategies to Improve Emissions and Efficiency of High Compression Ratio Diesel Engines

2008-10-06
2008-01-2472
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.
Technical Paper

Heat Release Analysis of Clean Combustion with Ethanol Ignited by Diesel in a High Compression Ratio Engine

2016-04-05
2016-01-0766
The control of nitrogen oxide and smoke emissions in diesel engines has been one of the key researches in both the academia and industry. Nitrogen oxides can be effectively suppressed by the use of exhaust gas recirculation (EGR). However, the introduction of inert exhaust gas into the engine intake is often associated with high smoke emissions. To overcome these issues there have been a number of proposed strategies, one of the more promising being the use of low temperature combustion enabled with heavy EGR. This has the potential to achieve simultaneously low emissions of nitrogen oxide and smoke. However, a quantitative way to identify the transition zone between high temperature combustion and low temperature combustion has still not been fully explored. The combustion becomes even more complicated when ethanol fuel is used as a partial substitution for diesel fuel.
Journal Article

Heat Release Pattern Diagnostics to Improve Diesel Low Temperature Combustion

2008-06-23
2008-01-1726
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.
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