Search Results

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.

It is well-known that gasoline is a poor fuel for HCCI operation due to its high autoignation temperature, while the major problem for diesel HCCI is that the ignition temperature of diesel fuel is too low so that diesel autoignites too early. Interestingly a blend of gasoline and diesel fuel could have desirable characteristics for HCCI operation. The negative valve overlap (NVO) is a practical and feasible control mode for production applications of the HCCI concept. At present, the most serious problem is the difficulty to control the moment of auto-ignition and extend the limited operating window of smooth HCCI operation. In this paper, the promotive effects of diesel fuel on gasoline HCCI combustion were experimentally examined. The diesel fuel as additive was added in advance in different proportion (10% and 20% by mass) into gasoline for the purpose of improving its ignitability. The experiments conducted on a gasoline HCCI engine which was naturally aspirated and unthrottled.

Gasoline and diesel, the two fuels with very different characteristics and with wide availability for conventional engine use, were blended as a HCCI engine fuel. Gasoline, with high volatility, easy vaporization and mixture formation, is used to form the homogeneous charge. Diesel fuel which has good ignitability and fast combustion at the conditions predominating in the HCCI environment, is used to dominate the auto-ignition and restrain the knocking combustion. It is expected that these two different fuels with opposite but complementary properties can be used to reach a good compromise in HCCI combustion. Experiments, conducted with moderate compression ratios (CR) and using two modes of HCCI control, i.e. intake heating with CR 15.0 and negative valve overlap (NVO) with CR 10.4, yielded results that prove this expectation.

Liquefied alternative fuels offer great potential benefits in reducing exhaust emissions and improving fuel economy of automotive engines. In order to achieve the best performance of the engine running with such fuels, it is critical to have an appropriate fuel system. In the present work, a new electronically controlled common-rail injection system has been specially designed and tested for the direct injection of liquefied alternative fuels, since a conventional pump-line-injector injection system in the conventional diesel engine was not suitable for the purpose. Experimental work has been carried out to examine and improve matching of the fuel injection system on a new fuel injection pump test bench. The preliminary engine bench test has demonstrated that this arrangement meets the requirement for the operating characteristics of a fuel injection system in a direct injection diesel engine operating with dimethyl ether (DME).

With boosted HCCI operation on gasoline using residual gas trapping, the amount of residuals was found to be of importance in determining the boundaries of stable combustion at various boost pressures. This paper represents a development of this approach by concentrating on the effects of inlet valve events on the parameters of boosted HCCI combustion with residual gas trapping. It was found that an optimum inlet valve timing could be found in order to minimize NOx emissions. When the valve timing is significantly advanced or retarded away from this optimum, NOx emissions increase due to the richer air / fuel ratios required for stable combustion. These richer conditions are necessary as a result of either the trapped residual gases becoming cooled in early backflow or because of lowering of the effective compression ratio. The paper also examines the feasibility of using inlet valve timing as a method of controlling the combustion phasing for boosted HCCI with residual gas trapping.

The application of Homogeneous Charge Compression Ignition (HCCI) combustion to naturally aspirated engines has shown a much reduced usable load range as compared to spark ignition (SI) engines. The approach documented here applies inlet charge boosting to gasoline HCCI operation on an engine configuration that is typical for SI gasoline engines, in conjunction with residual gas trapping. The latter helps to retain the benefits of much reduced requirement for external heating. In the present work, the achievable engine load range is controlled by the level of boost pressure while varying the amount of trapped residual gas. In addition, it was found that there is a maximum amount of boost that can be applied without intake heating for any given amount of trapped residuals. NOx emissions decrease with increasing amounts of trapped residual.

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.

Low-temperature heat release (LTHR) in spark-ignited internal combustion engines is a critical step toward the occurrence of auto-ignition, which can lead to an undesirable phenomenon known as engine knock. Hence, correct predictions of LTHR are of utmost importance to improve the understanding of knock and enable techniques aimed at controlling it. While LTHR is typically obscured by the deflagration following the spark ignition, extremely late ignition timings can lead to LTHR occurrence prior to the spark, i.e., pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection SI engine was numerically investigated using three-dimensional computational fluid dynamics (CFD). A hybrid approach was used, based on the G-equation model for representing the turbulent flame front and the multi-zone well-stirred reactor model for tracking the chemical reactions within the unburnt region.

n-butanol has been recognized as a promising alternative fuel for gasoline and may potentially overcome the drawbacks of methanol and ethanol, e.g. higher energy density. In this paper, the spray characteristics of gasoline and n-butanol have been investigated using a high pressure direct injection injector. High speed imaging and Phase Doppler Particle Analyzer (PDPA) techniques were used to study the spray penetration and the droplet atomization process. The tests were carried out in a high pressure constant volume vessel over a range of injection pressure from 60 to 150 bar and ambient pressure from 1 to 5 bar. The results show that gasoline has a longer penetration length than that of n-butanol in most test conditions due to the relatively small density and viscosity of gasoline; n-butanol has larger SMD due to its higher viscosity. The increase in ambient pressure leads to the reduction in SMD by 42% for gasoline and by 37% for n-butanol.

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.

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.

The use of deposit control additives in European market gasoline is well documented for maintaining high levels of engine cleanliness and subsequent sustained fuel and emissions performance. Co-ordinating European Council (CEC) industry fuels tests have played a crucial role in helping to drive market relevant, effective and low-cost deposit control additives into European market fuels. Until now, there hasn’t been a Gasoline Direct Injection engine test available to fuel marketers in any market globally. However, a new CEC engine test is currently being developed to address that gap. Based on an in-house VW injector coking test, it shows promise for becoming a useful tool with which to develop and measure the performance of deposit control additives. A key requirement of industry tests should be to replicate issues seen in consumer vehicles, thereby providing a platform for relevant solutions.