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Technical Paper

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

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

Fuel Burn Rate Control to Improve Load Capability of Neat n-Butanol Combustion in a Modern Diesel Engine

This research work investigates the control strategies of fuel burn rate of neat n-butanol combustion to improve the engine load capability. Engine tests of homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) with neat n-butanol show promising NOx and smoke emissions; however, the rapid burn rate of n-butanol results in excessive pressure rise rates and limits the engine load capability. A multi-event combustion strategy is developed to modulate the fuel burn rate of the combustion cycle and thus to reduce the otherwise high pressure rise rates at higher engine load levels. In the multi-event combustion strategy, the first combustion event is produced near TDC by the compression ignition of the port injected butanol that resembles the HCCI combustion; the second combustion event occurs near 7~12 degrees after TDC, which is produced by butanol direct injection (DI) after the first HCCI-like combustion event.
Technical Paper

Ignition Improvement of Premixed Methane-Air Mixtures by Distributed Spark Discharge

In order to improve the fuel economy for future high-efficiency spark ignition engines, the use of advanced combustion strategies with an overall lean and/or exhaust gas recirculation diluted cylinder charge is deemed to be beneficial, provided a reliable ignition process available. In this paper, experimental results of igniting methane-air mixture by means of capacitive coupled ignition and multi-coil distributed spark ignition are presented. It is found that with a conventional spark plug electrode configuration, increase of spark energy does not proportionally enhance the ignition flame kernel development. The use of capacitive coupled ignition to enhance the initial transient power resulted in faster kernel growth compared to the conventional system. The distribution of the spark energy across a number of spark gaps shows considerable benefit.
Technical Paper

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

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

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

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

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.
Technical Paper

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

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

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

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

An Enabling Study of Diesel Low Temperature Combustion via Adaptive Control

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

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

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

Diesel EGR Fuel Reformer Improvement with Flow Reversal and Central Fueling

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.
Journal Article

An Improvement on Low Temperature Combustion in Neat Biodiesel Engine Cycles

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

Low Temperature Combustion of Neat Biodiesel Fuel on a Common-rail Diesel Engine

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.
Technical Paper

Thermal Efficiency Analyses of Diesel Low Temperature Combustion Cycles

Thermal efficiency comparisons are made between the low temperature combustion and the conventional diesel cycles on a common-rail diesel engine with a conventional diesel fuel. Empirical studies have been conducted under independently controlled exhaust gas recirculation, intake boost, and exhaust backpressure. Up to 8 fuel injection pulses per cylinder per cycle have been applied to modulate the homogeneity history of the early injection diesel low temperature combustion operations in order to improve the phasing of the combustion process. The impact of heat release phasing, duration, shaping, and splitting on the thermal efficiency has been analyzed with zero-dimensional engine cycle simulations. This paper intends to identify the major parameters that affect diesel low temperature combustion engine thermal efficiency.
Technical Paper

An Investigation of EGR Treatment on the Emission and Operating Characteristics of Modern Diesel Engines

Tests are conducted to improve the use of exhaust gas recirculation on a single cylinder diesel engine with EGR stream treatment techniques that include intake heating, combustible substance oxidation, catalytic fuel reforming, and partial bypass-flow control. In parallel with the empirical work, theoretical modeling analyses are performed to investigate the effectiveness of the reforming process and the combined effects on the overall system efficiency. The research is aimed at stabilizing and expanding the limits of heavy EGR during steady and transient operations so that the individual limiting conditions of EGR can be better identified. Additionally, the heavy EGR is applied to enable in-cylinder low temperature combustion. The effectiveness of EGR treatment on engine emission and operating characteristics are therefore reported.
Technical Paper

Neat Biodiesel Fuel Engine Tests and Preliminary Modelling

Engine performance and emission comparisons were made between the use of 100% soy, Canola and yellow grease derived biodiesel fuels and an ultra-low sulphur diesel fuel in the oxygen deficient regions, i.e. full or high load engine operations. Exhaust gas recirculation (EGR) was extensively applied to initiate low temperature combustion. An intake throttling valve was implemented to increase the differential pressure between the intake and exhaust in order to increase and enhance the EGR. The intake temperature, pressure, and EGR levels were modulated to improve the engine fuel efficiency and exhaust emissions. Furthermore, a preliminary ignition delay correlation under the influence of EGR was developed. Preliminary low temperature combustion modelling of the biodiesel and diesel fuels was also conducted. The research intends to achieve simultaneous reductions of nitrogen oxides and soot emissions in modern production diesel engines when biodiesel is applied.
Technical Paper

Influence of Biodiesel Fuel on Diesel Engine Performance and Emissions in Low Temperature Combustion

The exhaust emission and performance characteristics of a 100% biodiesel fuel was evaluated on a single cylinder direct injection diesel engine that had been modified to allow multi-pulse diesel fuel injection at the intake port and independent control of intake heating, exhaust gas recirculation and throttling. Firstly, conventional single-shot direct injection tests were conducted and comparisons made between the use of an ultra-low sulphur diesel fuel and the biodiesel fuel. Secondly, tests for the premixed combustion of neat biodiesel were performed. Exhaust gas recirculation was applied extensively to initiate the low temperature combustion for the conventional in-cylinder single injection operation and to moderate the timing of the homogeneous charge compression ignition for the intake-port sequential injection. Because of the high viscosity and low volatility of the biodiesel, pilot-ignited homogeneous charge compression ignition was used.