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This paper presents a computational investigation of the in-cylinder charge characteristics within a motored 4-valve direct injection HCCI engine cylinder with applied negative valve overlapping. Non-typical intake valve strategy was investigated; whereby the pair of intake valves was assumed to follow the same low-lift short-duration valve-lift profile but actuated at different timings. The phase of intake-valve-opening relative to that of exhaust-valve-closing was optimized in terms of pumping losses. The flow fields generated with such an intake valve strategy were compared to those produced in the same engine cylinder but with typical early and late intake-valve-timing. The computational results of such an approach showed modifications in the in-cylinder swirl and tumble motions during the intake and compression strokes.

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.

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).

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.

Combustion behaviour and emissions characteristics of different blending ratios of diesel and gasoline fuels (Dieseline) were investigated in a light-duty 4-cylinder compression-ignition (CI) engine operating on partially premixed compression ignition (PPCI) mode. Experiments show that increasing volatility and reducing cetane number of fuels can help promote PPCI and consequently reduce particulate matter (PM) emissions while oxides of nitrogen (NOx) emissions reduction depends on the engine load. Three different blends, 0% (G0), 20% (G20) and 50% (G50) of gasoline mixed with diesel by volume, were studied and results were compared to the diesel-baseline with the same combustion phasing for all experiments. Engine speed was fixed at 1800rpm, while the engine load was varied from 1.38 to 7.85 bar BMEP with the exhaust gas recirculation (EGR) application.

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 near-field diesel spray process in diesel engines is the intermediate one that connects the in-nozzle flow with far field spray process and high-speed imaging techniques with high-quality temporal and spatial resolution are required in order to record this short process (< 300 μs). In this study, a high-speed charge-coupled-device (CCD) camera with the speed of up to 1,000,000 fps was used to study the near-field spray process for a diesel injector with different nozzle diameters. The tests were carried out in a constant volume vessel over a range of injection pressure and ambient pressure in non-evaporating conditions. The observed zone of the spray was where penetration length is less than 18 mm. The development of spray penetration length against time after start of injection (ASOI) was used to evaluate the spray process. The significant difference on spray penetration length development is found when the nozzle diameter varied.

A study of Multiple Premixed Compression Ignition (MPCI) with heavy naphtha is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the net indicated mean effective pressure (IMEP) from 0.5MPa to 0.9MPa. Commercial diesel is also tested with the single injection for reference. The combustion and emissions characteristics of the heavy naphtha are investigated by sweeping the first (−200 ∼ −20 deg ATDC) and the second injection timing (−5 ∼ 15 deg ATDC) with an injection split ratio of 50/50. The results show that compared with diesel combustion, the naphtha MPCI can reduce NOx, soot emissions and particle number simultaneously while maintaining or achieving even higher indicated thermal efficiency. A low pressure rise rate can be achieved due to the two-stage combustion character of the MPCI mode but with the penalty of high HC and CO emissions, especially at 0.5MPa IMEP.

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.

Exhaust Gas Fuel Reforming has potential to be used for on-board generation of hydrogen rich gas, reformate, and to act as an energy recovery system allowing the capture of waste exhaust heat. High exhaust gas temperature drives endothermic reforming reactions that convert hydrocarbon fuel into gaseous fuel when combined with exhaust gas over a catalyst - the result is an increase in overall fuel energy that is proportional to waste energy capture. The paper demonstrates how the combustion of reformate in a direct injection gasoline (GDI) engine via Reformed Exhaust Gas Recirculation (REGR) can be beneficial to engine performance and emissions. Bottled reformate was inducted into a single cylinder GDI engine at a range of engine loads to compare REGR to conventional EGR. The reformate composition was selected to approximate reformate produced by exhaust gas fuel reforming at typical gasoline engine exhaust temperatures.

Dieseline combustion as a concept combines the advantages of gasoline and diesel by offline or online blending the two fuels. Dieseline has become an attractive new compression ignition combustion concept in recent years and furthermore an approach to a full-boiling-range fuel. High speed imaging with near-parallel backlit light was used to investigate the spray characteristics of dieseline and pure fuels with a common rail diesel injection system in a constant volume vessel. The results were acquired at different blend ratios, and at different temperatures and back pressures at an injection pressure of 100MPa. The penetrations and the evaporation states were compared with those of gasoline and diesel. The spray profile was analyzed in both area and shape with statistical methods. The effect of gasoline percentage on the evaporation in the fuel spray was evaluated.

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.

Research studies show that 2-methylfuran (MF) is a promising gasoline alternative regarding its positive effect on engine performance and emissions. Before using pure MF in spark ignition engines, it is more likely to be used in a low-level blended form in gasoline. An experimental research study was carried out to investigate the impacts of low-level MF content in gasoline (volumetric 10% MF in blend) on direct-injection spark-ignition (DISI) engine combustion behavior and emissions. The tests were conducted on a single-cylinder spray-guided DISI research engine at an engine speed of 1500 rpm under stoichiometric conditions. The engine loads of 3.5 ~ 8.5 bar IMEP were tested and gasoline-optimized spark timing was used. Furthermore, the effects of spark timing, exhaust gas recirculation (EGR) and valve overlap on NOx emissions were tested.

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.

Negative valve overlapping is widely used for trapping residual burned gas within the cylinder to enable controlled Homogeneous Charge Compression Ignition (HCCI). HCCI has been shown as a promising combustion technology to improve the fuel economy and NOx emissions of gasoline engines. While the importance of in-cylinder flow in the fuel and air mixing process is recognised, the characteristics of air motion with specially designed valve events having reduced valve lift and durations associated with HCCI engines and their effect on subsequent combustion are not yet fully understood. This paper presents an investigation in an optical engine designed for HCCI combustion using EGR trapping. PIV techniques have been used to measure the in-cylinder flow field under motored conditions and a quantitative analysis has been carried out for the flow characterisation with comparison made against the flow in the same engine with conventional valve strategies for SI combustion.

Diesel engines are the versatile power source and is widely used in passenger car and commercial vehicle applications. Environmental temperature conditions, fuel quality, fuel injection strategies and lubricant have influence on cold start performance of the diesel engines. Strategies to overcome the cold start problem at very low ambient temperature include preheating of intake air, coolant, cylinder block. The present research work investigates the effect of coolant temperatures on passenger car diesel engine’s performance and exhaust emission characteristics during the cold start at cold ambient temperature conditions. The engine is soaked in the -7°C environment for 6 hours. The engine coolant is preheated to the desired coolant temperatures of 10 and 20°C by an external heater and the start ability tests were performed.

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.