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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

Distributed Electrical Discharge to Improve the Ignition of Premixed Quiescent and Turbulent Mixtures

The present work investigates the efficacy of distributed electrical discharge to increase the ignition volume by means of multipole spark discharge and radio frequency (RF) corona discharge. A range of ignition strategies are implemented to evaluate the efficacy of distributed ignition. The multipole spark igniter design has multiple high-voltage electrodes in close proximity to each other. This distributed spark ignition concept has the ability to generate multiple flame kernels either simultaneously or in a staggered mode. A novel elastic breakdown ignition strategy in responsive distribution (eBIRD) high frequency discharge is also implemented via the multipole igniter. The RF corona discharge is generated through an in-house developed ignition system. A form of distributed ignition is initiated along the streamer filaments.
Technical Paper

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

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

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

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

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

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

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.
Journal Article

Impact of Fuel Properties on Diesel Low Temperature Combustion

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.
Journal Article

Efficacy of EGR and Boost in Single-Injection Enabled Low Temperature Combustion

Exhaust gas recirculation, fuel injection strategy and boost pressure are among the key enablers to attain low NOx and soot emissions simultaneously on modern diesel engines. In this work, the individual influence of these parameters on the emissions are investigated independently for engine loads up to 8 bar IMEP. A single-shot fuel injection strategy has been deployed to push the diesel cycle into low temperature combustion with EGR. The results indicated that NOx was a stronger respondent to injection pressure levels than to boost when the EGR ratio is relatively low. However, when the EGR level was sufficiently high, the NOx was virtually grounded and the effect of boost or injection pressure becomes irrelevant. Further tests indicated that a higher injection pressure lowered soot emissions across the EGR sweeps while the effect of boost on the soot reduction appeared significant only at higher soot levels.
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

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.