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The effects of variable intake-valve-timing on the gas exchange process and performance of a 4-valve direct-injection HCCI engine were computationally investigated using a 1D gas dynamics engine cycle simulation code. A non-typical strategy to actuate the pair of intake valves was examined; whereby each valve was assumed to be actuated independently at different timing. Using such an intake valves strategy, the obtained results showed a considerable improvement of the engine parameters such as load and charging efficiency as compared with the typical identical intake valve pair timings case. Additional benefits of minimizing pumping losses and improving the fuel economy were demonstrated with the use of the non-simultaneous actuation of the intake valve pair having the opening timing of the early intake valve coupled with a symmetric degree of crank angle for the timing of exhaust valve closing.

For Homogeneous Charge Compression Ignition (HCCI) combustion, the auto-ignition process is very sensitive to in-cylinder conditions. This includes the change in in-cylinder temperature, the composition of chemical components and their concentrations. This sensitivity presents a major challenge for the accurate control of reliable and efficient HCCI combustion. This paper outlines our recent work: 1. a real-time control oriented gasoline-fueled HCCI combustion model and its implementation in Simulink with fixed step for the conversion into dSPACE Hardware-in-the-Loop (HIL) simulation purpose. 2. The development of model-based fast calibration for the best fuel efficiency and hydrocarbon emissions via evolutionary algorithm (EA). The model reported in this paper is able to run in real-time cycle-to-cycle under engine speeds below 4000rpm and with fixed simulation steps.

The major characteristics of the combustion in Homogeneous Charge Compression Ignition (HCCI) engines, irrespective of the technological strategy used to enable the ‘controlled auto-ignition’, are that the mixture of fuel and air is preferably premixed and largely homogeneous. Ignition tends to take place simultaneously at multiple points and there is no bulk flame propagation as in conventional spark-ignition (SI) engines. This paper presents an experimental study of flame development in an optical engine operating in HCCI combustion mode. High resolution and high-speed charge coupled device (CCD) cameras were used to take images of the flame during the combustion process. Fuels include gasoline, natural gas (NG) and hydrogen addition to NG all at stoichiometric conditions, permitting the investigation of combustion development for each fuel. The flame imaging data was supplemented by simultaneously recorded in-cylinder pressure data.

Using EGR instead of throttle to control the load of a stoichiometric dual-fuel dieseline (diesel and gasoline) compression ignition (SDCI) engine with three-way catalyst (TWC) aftertreatment is considered a promising technology to address the challenges of fuel consumption and emissions in future internal combustion engines. High-speed imaging is used to record the flame signal in a single-cylinder optical engine with a PFI+DI dual injection system. The premixed blue flame is identified and separated using green and blue channels in RGB images. The effects of injection timing on SDCI combustion are studied. An earlier injection strategy is found to be ideal for soot reduction; however, the ignition-injection decoupling problem results in difficulties in combustion control. It is also found that a split injection strategy has advantages in soot reduction and thermal efficiency.

There is an increasing recognition of injector deposit (ID) formation in fuel injection equipment as direct injection spark ignition (DISI) engine technologies advance to meet increasingly stringent emission legislation and fuel economy requirements. While it is known that the phenomena of ID in DISI engines can be influenced by changes in fuel composition, including increasing usage of aliphatic alcohols and additive chemistries to enhance fuel performance, there is however still a great deal of uncertainty regarding the physical and chemical structure of these deposits, and the mechanisms of deposit formation. In this study, a mechanical cracking sample preparation technique was developed to assess the deposits across DISI injectors fuelled with gasoline and blends of 85% ethanol (E85).

While Homogeneous Charge Compression Ignition (HCCI) is a promising combustion mode with significant advantages in fuel economy improvement and emission reductions for vehicle engines, it is subject to a number of limitations, for example, hardware and control complexity, or NOx and NVH deterioration near its operating upper load boundary, diminishing its advantages. Conventional spark-ignition combustion mode is required for higher loads and speeds, thus the operating conditions near the HCCI boundaries and their corresponding alternatives in SI mode must be studied carefully in order to identify practical strategies to minimise the impact of the combustion mode transition on the performance of the engine. This paper presents the results of an investigation of the combustion mode transitions between SI and HCCI, using a combination of an engine cycle simulation code with a chemical kinetics based HCCI combustion code.

For spark ignition (SI) engines, the optimum spark timing is crucial for maximum efficiency. However, as the spark timing is advanced, so the propensity to knock increases, thus compromising efficiency. One method to suppress knock is to use high octane fuel additives. However, the blend ratio of these additives cannot be varied on demand. Therefore, with the advent of aggressive downsizing, new knock mitigation techniques are required. Fortuitously, there are two well-known lower alcohols which exhibit attractive knock mitigation properties: ethanol and methanol. Both not only have high octane ratings, but also result in greater charge-cooling than with gasoline. In the current work, the authors have exploited these attractive properties with the dual-injection, or the dual-fuel concept (gasoline in PFI and fuel additive in DI) using pure ethanol and methanol.

The paper presents analysis of performance and emission characteristics of a common rail diesel engine operating with RME, with and without EGR. In both cases, the RME fuel was pre-heated in a heat exchanger to control its temperature before being pumped to the common rail. The studied parameters include the in-cylinder pressure history, rate of heat release, mass fraction burned, and exhaust emissions. The results show that when the fuel temperature increases and the engine is operated without EGR, the brake specific fuel consumption (bsfc) decreases, engine efficiency increases and NOx emission slightly decreases. However, when EGR is used while fuel temperature is increased, the bsfc and engine efficiency is independent of fuel temperature while NOx slightly increases.

Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve HCCI (homogeneous charge compression ignition) engine operation. Previous work by the authors has shown that hydrogen addition improves combustion stability in various difficult combustion conditions. It is shown here that hydrogen, together with residual gas trapping, helps also in lowering the intake temperature required for HCCI. It has been argued in literature that the addition of hydrogen advances the start of combustion in the cylinder. This would translate into the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke. The experimental results of this work show that, with hydrogen replacing part of the fuel, a decrease in intake air temperature requirement is observed for a range of engine loads, with larger reductions in temperature noted at lower loads.

Biodiesel is an oxygenated alternative fuel made from vegetable oils and animal fats via transesterification and the feedstock of biodiesel is diverse and varies between the local agriculture and market scenarios. Use of various feedstock for biodiesel production result in variations in the fuel properties of biodiesel. In this study, biodiesels produced from a variety of real world feedstock was examined to assess the performance and emissions in a light-duty engine. The objective was to understand the impact of biodiesel properties on engine performances and emissions. A group of six biodiesels produced from the most common feedstock blended with zero-sulphur diesel in 10%, 30% and 60% by volume are selected for the study. All the biodiesel blends were tested on a light-duty, twin-turbocharged common rail V6 engine. Their gaseous emissions (NOx, THC, CO and CO2) and smoke number were measured for the study.

Ethanol has long been regarded as the optimal gasoline-alternative biofuel for spark-ignition (SI) engines. It is used widely in Latin and North America and is increasingly accepted as an attractive option across Europe. Nevertheless, its low energy density requires a high rate of manufacture; in areas which are deficient of arable land, such rates might prove problematic. Therefore, fuels with higher calorific values, such as butanol or 2,5-dimethylfuran (DMF) deserve consideration; a similar yield to ethanol, in theory, would require much less land. This report addresses the suitability of DMF, to meet the needs as a biofuel substitute for gasoline in SI engines, using ethanol as the biofuel benchmark. Specific attention is given to the sensitivity of DMF to various engine control parameters: combustion phasing (ignition timing), injection timing, relative air-fuel ratio and valve timing (intake and exhaust).

Ethanol fuel blends with gasoline for spark ignition (SI) internal combustion engines are widely used on account of their advantages in terms of fuel economy and emissions reduction potential. The focus of this paper is to study the effects of these blends on combustion characteristics such as in-cylinder pressure profiles, gas-phase emissions (e.g., unburned hydrocarbons, NOx) and particulates (e.g., particulate matter and particle number) using both measurement campaigns and digital engineering workflows. Nineteen load-speed operating points in a 1L 3-cylinder GDI SI engine were measured and modelled. The measurements for in-cylinder pressure and emissions were repeated at each operating point for three types of fuel: gasoline (E0, 0% by volume of ethanol blend), E10 (10 % by volume of ethanol blend) and E20 (20% by volume of ethanol blend).

Injection pressure oscillations are proven to determine considerable deviations from the expected mass flow rate, leading to the jet velocities non-uniformity, which in turn implies the uneven spatial distribution of A/F ratio. Furthermore, once the injector is triggered, these oscillations might lead the rail pressure to experience a decreasing stage, to the detriment of spray penetration length, radial propagation and jet break-up timing. This has urged the research community to develop models predicting injection-induced pressure fluctuations within the rail. Additionally, several devices have been designed to minimize and eliminate such fluctuations. However, despite the wide literature dealing with the injection-induced pressure oscillations, many aspects remain still unclear. Moreover, the compulsory compliance with environmental regulations has shifted focus onto alternative fuels, which represent a promising pathway for sustainable vehicle mobility.

The demand for more efficient and clean engines have prompted the research and development of new engine technologies. Automotive engines expected to run with leaner mixtures and higher compression ratios. Lean burn is effective to increase fuel economy whilst reducing emissions but unreliable ignition of the lean mixtures by the conventional spark plug is one of the problems which causes concerns to the engine designers. Laser ignition is a promising technology and holds many benefits over the spark ignition because it can extend the ignitability of lean mixtures with flexibility of the ignition location and absence of electrode degradation for improved engine performance with lean burn. In this study, high-speed photography is used to investigate the flame kernel growth and propagation in an optical direct injection engine using laser ignition by an Nd:YAG laser.

The cold start performance of a diesel engine has been receiving more attention as the European Commission emission regulations directed to include cold start emissions in the legislative emission driving cycles. The cold start performance of diesel engines is influenced by the ambient temperature conditions, engine design, fuel, lubricant and engine operating conditions. The present research work investigates the effect of cold ambient conditions on the diesel engine's performance and the exhaust emission (gaseous and particulate emissions) characteristics during the cold start and followed by idle. The engine startability and idling tests were carried out on the latest generation of diesel engine in a cold cell at various ambient temperatures ranging between +20°C and −20°C. Higher fuel consumption and peak speed were observed at very cold ambient compared to those at normal ambient during the cold start.

Ambient temperature has significant impact on engine start ability and cold start emissions from diesel engines. These cold start emissions are accounted for substantial amount of the overall regulatory driving cycle emissions like NEDC or FTP. It is likely to implement the low temperature emissions tests for diesel vehicles, which is currently applicable only for gasoline vehicles. This paper investigates the potential of the intake heating strategy on reducing the driving cycle emissions from the latest generation of turbocharged common rail direct injection diesel engines at low ambient temperature conditions. For this investigation an air heater was installed upstream of the intake manifold and New European Driving Cycle (NEDC) tests were conducted at -7°C ambient temperature conditions for the different intake air temperatures. Intake air heating reduced the cranking time and improved the fuel economy at low ambient temperatures.

The bio-fuel, 2,5 - dimethylfuran (DMF) is currently regarded as a potential alternative fuel to gasoline due to the development of new production technology. However, little is known about the flame behavior in an optical engine. In this paper, high speed imaging (with intensifier) was used during the combustion of DMF and its blends with gasoline and ethanol (D50, D85, E50D50 and E85D15) in an SI optical engine. The flame images from the combustion of each fuel were analyzed at two engine loads: 3bar and 4bar IMEP. For DMF, D50 and E50D50, two modes were compared: DI and PFI. The average flame shapes (in 2D) and the average flame speeds were calculated and combined with mass fraction burned (MFB) data. The results show that when using DMF, the rate of flame growth development and flame speed is higher than when using gasoline. The differences in flame speed between DMF and gasoline is about 10% to 14% at low IMEP.

The combustion characteristics and soot emissions of three types of fuels were studied in a high pressure and temperature vessel. In order to achieve better volatility, proper cetane number and high oxygen content, the newly designed WDEP fuel was proposed and investigated. It is composed of wide distillation fuel (WD), PODE3-6 mixture (PODEn) and ethanol. For comparison, the test on WD and the mixture of PODEn-ethanol (EP) are also conducted. OH* chemiluminescence during the combustion was measured and instantaneous PLII was also applied to reveal the soot distribution. Abel transformation was adopted to calculate the total soot of axisymmetric flame. The results show that WDEP has similar ignition delays and flame lift-off lengths to those of WD at 870-920 K. But the initial ignition locations of WDEP flame in different cycles were more concentrated, particularly under the condition of low oxygen atmosphere.

Conventional diesel-fuelled Partially Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, dieseline (blending of diesel and gasoline) was looked into as the Partially Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated.

Little research has been done on spray characteristics of 2,5-dimethylfuran (DMF), since the breakthrough in its production method as an alternative fuel candidate. In this paper, the spray characteristics of pure fuels (DMF, Isooctane) and DMF-Isooctane blends under different ambient pressures (1 bar, 3 bar and 7 bar) and injection pressures (50 bar, 100 bar and 150 bar) were studied using Phase Doppler Particle Analyzer (PDPA) and high speed imaging. Droplet velocity, size distribution, spray angle and penetration of sprays were examined. Based on the results, DMF had larger SMD and penetration length than isooctane. The surface tension of fuel strongly influenced spray characteristics. Increasing the surface tension by 26 % resulted in 12 % increase in SMD. Higher ambient pressure increased the drag force, but SMD was not influenced by the increased drag force. However, the increased ambient pressure reduced the injection velocity and We number resulting in higher SMD.