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Technical Paper

Energy Enhanced Adaptive Spark Ignition for Lean Combustion Initiation

2020-04-14
2020-01-0841
For internal combustion engine systems, lean and diluted combustion is an important technology applied for fuel efficiency improvement. Because of the thermodynamic boundary conditions and the presence of in-cylinder flow, the development of a well-sustained flame kernel for lean combustion is a challenging task. Reliable spark discharge with the addition of enhanced delivered energy is thus needed at certain time durations to achieve successful combustion initiation of the lean air-fuel mixture. For a conventional transistor coil ignition system, only limited amount of energy is stored in the ignition coil. Therefore, both the energy of the spark discharge and the duration of the spark discharge are bounded. To break through the energy limit of the conventional transistor coil ignition system, in this work, an adaptive spark ignition system is introduced. The system has the ability to reconstruct the conductive ion channels whenever it is interrupted during the spark discharge.
Technical Paper

Combustion Characterization of Neat n-Butanol in an SI Engine

2020-04-14
2020-01-0334
Increasingly stringent emission standards have promoted the interest in alternate fuel sources. Because of the comparable energy density to the existing fossil fuels and renewable production, alcohol fuels may be a suitable replacement, or an additive to the gasoline/diesel fuels to meet the future emission standards with minimal modification to current engine geometry. In this research, the combustion characteristics of neat n-butanol are analyzed under spark ignition operation using a single cylinder SI engine. The fuel is injected into the intake manifold using a port-fuel injector. Two modes of charge dilution were used in this investigation to test the limits of stable engine operation, namely lean burn using excess fresh air and exhaust gas recirculation (EGR). The in-cylinder pressure measurement and subsequently, heat release analysis are used to investigate the combustion characteristics of the fuel under low load SI engine operation.
Technical Paper

Combustion Stability Improvement via Multiple Ignition Sites on a Production Engine

2020-04-14
2020-01-1115
For spark ignition (SI) engines, further improvement of engine efficiency has become the major development trend, and lean burn/EGR technologies, as well as intensified in-cylinder flow, need to be adapted to reach that target. Stronger ignition sources become more favorable under extreme lean/EGR conditions. Among the ignition technologies developed, multiple ignition sites technology has been proved to be an effective way to help with the initial flame kernel development. In this paper, a spark ignited 4-cylinder turbo-charged production engine is employed to investigate the impact of multiple ignition sites technology on engine performance under lean burn conditions. Four in-house designed 3-core sparkplugs are installed on the cylinders to replace traditional stock sparkplugs, in order to generate multiple ignition sites in the cylinders.
Technical Paper

Discharge Current Management for Diluted Combustion under Forced Flow Conditions

2020-04-14
2020-01-1118
Lean burn or EGR diluted combustion with enhanced charge motion is effective in improving the efficiency of spark ignition engines. However, the ignition process under these conditions is getting more challenging due to higher ignition energy required by the lean or diluted mixture, as well as the interactions of the gas flow on the flame kernel. Enhanced spark discharge energy is essential to initiate the combustion under these conditions. Moreover, the discharge process should be more carefully controlled to improve the effectiveness of the spark. In this study, spark ignition systems with boosted discharge energy are used to ignite diluted air-fuel mixture under forced flow conditions. The impacts of the discharge current level, the discharge duration and the discharge current profile on the ignition are investigated in detail using optical diagnosis.
Journal Article

Impact of Spark Plasma Length on Flame Kernel Development under Flow Condition

2020-04-14
2020-01-1114
Advanced ignition systems with enhanced discharge current have been extensively investigated in research, since they are highly regarded as having the potential to overcome challenges that arise when spark-ignition engines are running under lean or EGR diluted conditions. Local flow field is also of particular importance to improve the ignitability of the air-fuel mixture in SI engines as the spark plasma channel can be stretched by the flow across the spark gap, leading to longer plasma length, thus more thermal spark energy distributed to the air-fuel mixture in the vicinity of the spark plug. Research results have shown that a constantly high discharge current is effective to maintain a stable spark plasma channel with less restrikes and longer plasma holding period.
Technical Paper

Experimental Study on the Characteristics of Short Circuits and Restrikes of Spark Channels

2020-04-14
2020-01-1123
Ignition performance is critical for the implementation of diluted combustion for spark-ignition engines. The short circuit and restrike phenomena can influence the initial ignition volume and discharge duration which are important for the stable ignition processes. In this study, the short circuits and restrikes of spark channels are studied with various flow velocities, spark plug gaps and discharge energies. The development of the spark channels is captured by using the direct imaging technique with a CMOS camera equipped with an image intensifier. A multi-coil ignition system is designed to enable flexible control of discharge energies. The results show that the spark plug gap size is a critical parameter to suppress the phenomena of short circuits and restrikes. With the enlargement of spark plug gap, the maximum and average lengths of the spark channel effectively increase.
Technical Paper

An Investigation on the Regeneration of Lean NOX Trap Using Dimethyl Ether

2020-04-14
2020-01-1354
The ever-stringent emission regulations are major challenges for the diesel fueled engines in automotive industry. The applications of advanced after-treatment technologies as well as alternative fuels [1] are considered as promising methodology to reduce exhaust emission from compression ignition (CI) engines. Using dimethyl ether (DME) as an alternative fuel has been extensively studied by many researchers and automotive manufactures since DME has demonstrated enormous potential in terms of emission reduction, such as low CO emission, and soot and sulfur free. However, the effect of employing DME in a lean NOX trap (LNT) based after-treatment system has not been fully addressed yet. In this work, investigations of the long breathing LNT system using DME as a reductant were performed on a heated after-treatment flow bench with simulated engine exhaust condition.
Technical Paper

Combustion and Emission Characteristics of SI and HCCI Combustion Fueled with DME and OME

2020-04-14
2020-01-1355
DME has been considered an alternative fuel to diesel fuel with promising benefits because of its high reactivity and volatility. Research shows that an engine fueled with DME will produce zero smoke emissions. However, the storage and the handling of the fuel are underlying difficulties owing to its high vapour pressure (530 kPa @ 20 °C). In lieu, OME1 fuel, a derivate of DME, offers advantages exhibited with DME fuel, all the while being a liquid fuel for engine application. In this work, engine tests are performed to realize the combustion behaviour of DME and OME1 fuel on a single-cylinder research engine with a compression ratio of 9.2:1. The dilution ratio of the mixture is progressively increased in two manners, allowing more air in the cylinder and applying exhaust gas recirculation (EGR). The high reactivity of DME suits the capability to be used in compression ignition combustion whereas OME1 must be supplied with a supplemental spark to initiate the combustion.
Technical Paper

A Framework for the Active Control of Corona Ignition Systems

2019-12-19
2019-01-2157
Corona ignition is a promising technology that has been demonstrated to be capable of improving the reliability of lean combustion. However, arcing is unavoidable during corona discharge. The high current surge during arcing can cause excessive damage to the corona ignition system. In this work, a control framework is proposed to help reduce and prevent arcing from happening in a corona ignition system. Experimental results are demonstrated to show the effectiveness of the proposed methodology.
Journal Article

Electrical Waveform Measurement of Spark Energy and its Effect on Lean Burn SI Engine Combustion

2019-12-19
2019-01-2159
The conventional transistor coil ignition system with coil-out energy up to 100 mJ might not be sufficient to establish a self-sustained flame kernel under lean combustion with strong in-cylinder flow motion. Further increase of the discharge current will decrease the voltage across the spark gap, which will affect the calculation of the energy delivered to the spark gap. In this paper, the relationship between the discharge current and gap voltage is investigated, and it is discovered that the spark energy doesn,t increase monotonously with the increase of the discharge current. However, engine test results still indicate a positive impact of discharge current amplitude on the engine performance.
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

A Study of Energy Enhanced Multi-Spark Discharge Ignition in a Constant-Volume Combustion Chamber

2019-04-02
2019-01-0728
Multi-spark discharge (MSD) ignition is widely used in high-speed internal combustion engines such as racing cars, motorcycles and outboard motors in attempts to achieve multiple sparks during each ignition. In contrast to transistor coil ignition (TCI) system, MSD system can be greatly shortened the charging time in a very short time. However, when the engine speed becomes higher, the ignition will be faster, electrical energy stored in the ignition system will certainly become less, especially for MSD system. Once the energy released into the spark plug gap can’t be guaranteed sufficiently, ignition will become more difficult, and it will get worse in some harsh environment such as strong turbulence or lean fuel conditions. With these circumstances, the risks of misfire and partial combustion will increase, which can deteriorate the power outputs and exhaust emissions of internal combustion engine.
Technical Paper

Preliminary Testing of n-Butanol HCCI on High Compression Ratio Diesel Engines

2019-04-02
2019-01-0577
The control of combustion phasing in homogeneous charge compression ignition (HCCI) combustion is investigated with neat n-butanol in this work. HCCI is a commonly researched combustion mode, owing to its improved thermal efficiency over conventional gasoline combustion, as well as its lower nitrogen oxide (NOx) and particulate matter emissions compared to those of diesel combustion. Despite these advantages, HCCI lacks successful widespread implementation with conventional fuels, primarily due to the lack of effective combustion phasing control. In this preliminary study, chemical kinetic simulations are conducted to study the auto-ignition characteristics of n-butanol under varied background pressures, temperatures, and dilution levels using established mechanisms in CHEMKIN software. Increasing the pressure or temperature lead to a shorter ignition delay, whereas increasing the dilution by the application of exhaust gas recirculation (EGR) leads to a longer ignition delay.
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

A Preliminary Study of the Discharge Current and Spark Energy for the Multi-Coil Offset Strategy

2019-04-02
2019-01-0725
To overcome the unfavorable operation conditions caused by lean/diluted charges in modern Spark Ignited (SI) engines, various advanced ignition systems have been proposed in the past. Among them, the dual-coil and multi-coil Transistor Coil Ignition (TCI) systems with offset discharge strategy caused significant attention in literature because they can generate a continuous spark with high spark energy being delivered into the cylinder. Comparing with the dual-coil system, a multi-coil system is capable to apply more flexible control strategies and generate a higher discharge current. However, the spark energy and transfer efficiency of the multi-coil system are still worthy to investigate as they are important performance indicators for a TCI system. In this paper, the discharge characteristics of the dual-coil and triple-coil strategies under both quiescent and flow conditions were studied firstly by experimental methods.
Technical Paper

Effects of Spark Discharge Energy Scheduling on Flame Kernel Formation under Quiescent and Flow Conditions

2019-04-02
2019-01-0727
The breakdown phase is considered to have the highest electric-thermal energy transfer efficiency among all the discharge modes in a conventional spark ignition process. In this study, an external capacitor is connected in parallel with the spark plug in order to enhance the discharge energy and power during the breakdown phase. A constant volume combustion chamber is used to investigate the high power spark discharge under different background pressures and with varied flow velocities. Results show that the added parallel capacitance is effective in redistributing the spark energy. With the increase in parallel capacitance, the breakdown power and energy increase, though at the cost of reduced glow phase energy. The breakdown energy also increases with the increased background pressure. Then combustion tests are carried out to study the effects of the breakdown power enhanced spark on flame propagation under both quiescent and flow conditions via optical diagnosis.
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.
Technical Paper

Boosted Current Spark Strategy for Lean Burn Spark Ignition Engines

2018-04-03
2018-01-1133
Spark ignition systems with the capability of providing spark event with either higher current level or longer discharge duration has been developed in recent years to help IC engines towards clean combustion with higher efficiency under lean/diluted intake charge. In this research, a boosted current spark strategy was proposed to investigate the effect of spark discharge current level and discharge duration on the combustion process. Firstly, the discharge characteristics of a boosted current spark system were tested with a traditional spark plug under crossflow conditions, and results showed that the spark channel was more stable, and was stretched much longer when the discharge current was boosted. Then the boosted current strategy was used in a spark ignition engine operating under lean conditions. Boosted current was added to the spark channel with different timing, duration, and current levels.
Technical Paper

Ion Current Measurement of Diluted Combustion Using a Multi-Electrode Spark Plug

2018-04-03
2018-01-1134
Close-loop feedback combustion control is essential for improving the internal combustion engines to meet the rigorous fuel efficiency demands and emission legislations. A vital part is the combustion sensing technology that diagnoses in-cylinder combustion information promptly, such as using cylinder pressure sensor and ion current measurement. The promptness and fidelity of the diagnostic are particularly important to the potential success of using intra-cycle control for abnormal cycles such as super knocking and misfiring. Many research studies have demonstrated the use of ion-current sensing as feedback signal to control the spark ignition gasoline engines, with the spark gap shared for both ignition and ion-current detection. During the spark glow phase, the sparking current may affect the combustion ion current signal. Moreover, the electrode gap size is optimized for sparking rather than measurement of ion current.
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.
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