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Technical Paper

Prompt Heat Release Analysis to Improve Diesel Low Temperature Combustion

2009-06-15
2009-01-1883
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.
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.
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

Empirical and Theoretical Investigations of Active-flow Control on Diesel Engine After-treatment

2006-04-03
2006-01-0465
Empirical and theoretical studies are made between active-flow control and passive-flow control schemes in investigating the influences of gas flow, heat transfer, chemical reaction, oxygen concentration, and substrate properties. The exhaust active-flow control includes the parallel alternating flow, partial restricting flow, periodic flow reversal, and extended flow stagnation that are found to be especially effective to treat engine exhausts that are difficult to cope with conventional passive-flow converters [1, 2]. The tests are set up on a single cylinder Yanmar engine. Theoretical studies are performed with the one-dimensional transient modeling techniques to analyze the thermal behavior of the diesel after-treatment systems when active flow control schemes are applied.
Technical Paper

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

2014-04-01
2014-01-1298
Abstract 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

The Impact of Intake Dilution and Combustion Phasing on the Combustion Stability of a Diesel Engine

2014-04-01
2014-01-1294
Abstract 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.
Technical Paper

Spark Ignition Circuit Energy Characterization based on a Simplified Model and Measurement Analysis

2015-04-14
2015-01-1271
Abstract The spark ignition circuit inside an internal combustion engine system is the source which provides the initiation energy required for triggering combustion in a spark ignition (SI) engine in-cylinder air/fuel mixture. Proper spark phasing and adequate spark energy release in spark ignited combustion would yield significant combustion efficiency improvement and affect the in-cylinder production species composition. In this work a simplified spark ignition circuit model constructed based on circuit theorems is proposed. Measurements on how ignition pressure, secondary circuit series resistance and dwell duration would affect the ignition energy migration are presented. Simulations using the proposed model have also demonstrated similar energy migration trends to measurement results which show the influences caused by different secondary series resistance and dwell durations.
Technical Paper

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

2015-04-14
2015-01-0803
Abstract 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.
Journal Article

Impact of Fuelling Techniques on Neat n-Butanol Combustion and Emissions in a Compression Ignition Engine

2015-04-14
2015-01-0808
Abstract 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.
Technical Paper

Efficiency and Emission Trade-Off in Diesel-Ethanol Low Temperature Combustion Cycles

2015-04-14
2015-01-0845
Abstract An experimental investigation of low temperature combustion (LTC) cycles is conducted with diesel and ethanol fuels on a high compression ratio (18.2:1), common-rail diesel engine. Two LTC modes are studied; near-TDC injection of diesel with up to 60% exhaust gas recirculation (EGR), and port injected ethanol ignited by direct injection of diesel with moderate EGR (30-45%). Indicated mean effective pressures up to 10 bar in the diesel LTC mode and 17.6 bar in the dual-fuel LTC mode have been realized. While the NOx and smoke emissions are significantly reduced, a thermal efficiency penalty is observed from the test results. In this work, the efficiency penalty is attributed to increased HC and CO emissions and a non-conventional heat release pattern. The influence of heat release phasing, duration, and shape, on the indicated performance is explained with the help of parametric engine cycle simulations.
Journal Article

Active Injection Control for Enabling Clean Combustion in Ethanol-Diesel Dual-Fuel Mode

2015-04-14
2015-01-0858
Abstract In this work, an active injection control strategy is developed for enabling clean and efficient combustion on an ethanol-diesel dual-fuel engine. The essence of this active injection control is the minimization of the diffusion burning and resultant emissions associated with the diesel injection while maintaining controllability over the ignition and combustion processes. A stand-alone injection bench is employed to characterize the rate of injection for the diesel injection events, and a regression model is established to describe the injection timings and injector delays. A new combustion control parameter is proposed to characterize the extent of diffusion burning on a cycle-to-cycle basis by comparing the modelled rate of diesel injection with the rate of heat release in real time. The test results show that the proposed parameter, compared with the traditional ignition delay, better correlates to the enabling of low NOx and low smoke combustion.
Technical Paper

Energy Efficiency Comparison between Butanol and Ethanol Combustion with Diesel Ignition

2015-04-14
2015-01-0859
Abstract 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.
Technical Paper

An Enabling Study of Neat n-Butanol HCCI Combustion on a High Compression-ratio Diesel Engine

2015-03-10
2015-01-0001
Abstract This work investigates the benefits and challenges of enabling neat n-butanol HCCI combustion on a high compression ratio (18.2:1) diesel engine. Minor engine modifications are made to implement n-butanol port injection while other engine components are kept intact. The impacts of the fuel change, from diesel to n-butanol, are examined through steady-state engine tests with independent control of the intake boost and exhaust gas recirculation. As demonstrated by the test results, the HCCI combustion of a thoroughly premixed n-butanol/air lean mixture offers near-zero smoke and ultralow NOx emissions even without the use of exhaust gas recirculation and produces comparable engine efficiencies to those of conventional diesel high temperature combustion. The test results also manifest the control challenges of running a neat alcohol fuel in the HCCI combustion mode.
Technical Paper

Study of Low Temperature Combustion with Neat n-Butanol on a Common-rail Diesel Engine

2015-03-10
2015-01-0003
Abstract 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.
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

Renewable Ethanol Use for Enabling High Load Clean Combustion in a Diesel Engine

2013-04-08
2013-01-0904
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.
Journal Article

Impact of Fuel Properties on Diesel Low Temperature Combustion

2011-04-12
2011-01-0329
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.
Technical Paper

Ignition Control of Gasoline-Diesel Dual Fuel Combustion

2012-09-24
2012-01-1972
The use of gasoline fuels in compression ignition engines, with or without diesel pilots, has shown encouraging progress in engine efficiency and emissions. The dual fuel combustion of gasoline-diesel offers the flexibility of modulating the cylinder charge reactivity, but an accurate and reliable control over the ignition in the dual fuel applications is more challenging than in classical engines. In this work, the gasoline-diesel dual fuel operation is investigated on a single cylinder research engine. The effects of the intake boost, exhaust gas recirculation (EGR) rates, diesel/gasoline ratio, and diesel injection timing are studied in regard to the ignition control. The results indicate that at low load, a diesel pilot can improve the cylinder charge reactivity and reduce emissions of incomplete combustion products.
Technical Paper

Low Temperature Combustion Strategies for Compression Ignition Engines: Operability limits and Challenges

2013-04-08
2013-01-0283
Low temperature combustion (LTC) strategies such as homogeneous charge compression ignition (HCCI), smokeless rich combustion, and reactivity controlled compression ignition (RCCI) provide for cleaner combustion with ultra-low NOx and soot emissions from compression-ignition engines. However, these strategies vary significantly in their implementation requirements, combustion characteristics, operability limits as well as sensitivity to boundary conditions such as exhaust gas recirculation (EGR) and intake temperature. In this work, a detailed analysis of the aforementioned LTC strategies has been carried out on a high-compression ratio, single-cylinder diesel engine. The effects of intake boost, EGR quantity/temperature, engine speed, injection scheduling and injection pressure on the operability limits have been empirically determined and correlated with the combustion stability and performance metrics.
Technical Paper

Exhaust Hydrocarbon Speciation from a Single-Cylinder Compression Ignition Engine Operating with In-Cylinder Blending of Gasoline and Diesel Fuels

2012-04-16
2012-01-0683
Diesel aided by gasoline low temperature combustion offers low NOx and low soot emissions, and further provides the potential to expand engine load range and improve engine efficiency. The diesel-gasoline operation however yields high unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. This study aims to correlate the chemical origins of the key hydrocarbon species detected in the engine exhaust under diesel-gasoline operation. It further aims to help develop strategies to lower the hydrocarbon emissions while retaining the low NOx, low soot, and efficiency benefits. A single-cylinder research engine was used to conduct the engine experiments at a constant engine load of 10 bar nIMEP with a fixed engine speed of 1600 rpm. Engine exhaust was sampled with a FTIR analyzer for speciation investigation.
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