Effects of hydrogen addition on high-pressure nonpremixed natural gas combustion

The effects of hydrogen addition on the ignition and combustion of a high-pressure methane jet in a quiescent charge of high-temperature, medium-pressure air were investigated numerically and experimentally. Subsequently, the results of these two fundamental studies were applied to the interpretation of combustion and emissions measurements from a pilot-ignited natural gas engine fueled with similar fuels. Whereas, under quiescent conditions, the influence of hydrogen addition on the autoignition delay time of the gaseous jet was small, a markedly greater effect was observed in the more complex environment of the research engine. Similarly, in the two fundamental studies, the addition of hydrogen to the methane fuel resulted in a reduction of NOx emissions, whereas increased levels of NOx emissions were observed from the engine, highlighting the difference between the autoignition and pilot-ignition process

Combustion in a heavy-duty direct-injection engine using hydrogen–methane blend fuels

Adding hydrogen to the fuel in a direct injection natural gas engine offers the potential significantly to reduce local and global air pollutant emissions. This work reports on the effects of fuelling a heavy-duty engine with late-cycle direct injection of blended hydrogen– methane fuels and diesel pilot ignition over a range of engine operating conditions. The effect of hydrogen on the combustion event varies with operating condition, providing insight into the fundamental factors limiting the combustion process. Combustion stability is enhanced at all conditions studied; this leads directly to a significant reduction in emissions of combustion byproducts, including carbon monoxide, particulate matter, and unburned fuel. Carbon dioxide emissions are also significantly reduced by the lower carbon–energy ratio of the fuel. The results suggest that this technique can significantly reduce both local and global pollutant emissions associated with heavy-duty transport applications while requiring minimal changes to the fuelling system

Hydrogen-methane blend fuelling of a heavy-duty, direct-injection engine

Combining hydrogen with natural gas as a fuel for internal combustion engines provides an early opportunity to introduce hydrogen into transportation applications. This study investigates the effects of fuelling a heavy-duty engine with a mixture of hydrogen and natural gas injected directly into the combustion chamber. The combustion system, developed for natural gas fuelling, is not modified for blended hydrogen operation. The results demonstrate that hydrogen can have a significant beneficial effect in reducing emissions without affecting efficiency or requiring significant engine modifications. Combustion stability is enhanced through the higher reactivity of the hydrogen, resulting in reduced emissions of unburned methane. The fuel’s lower carbon:energy ratio also reduces CO2 emissions. These results combine to significantly reduce tailpipe greenhouse gas (GHG) emissions. However, the effect on net GHG’s, including both tailpipe and fuelproduction emissions, depends on the source of the hydrogen. Cleaner sources, such as electrolysis based on renewables and hydro-electric power, generate a significant net reduction in GHG emissions. Hydrogen generated by steam-methane reforming is essentially GHG neutral, while electrolysis using electricity from fossil-fuel power plants significantly increases net GHG emissions compared to conventional natural gas fuelling

The influence of fuel composition on a heavy-duty, natural-gas direct-injection engine

This work investigates the implications of natural gas composition on the combustion in a heavy-duty natural gas engine and on the associated pollutant emissions. In this engine system, natural gas is injected into the combustion chamber shortly before the end of the compression stroke; a diesel pilot that precedes the natural gas injection provides the ignition source. The effects of adding ethane, propane, hydrogen, and nitrogen to the fuel are reported here. The results indicate that these additives had no significant effect on the engine’s power or fuel consumption. Emissions of unburned fuel are reduced for all additives through either enhanced ignition or combustion processes. Black carbon particulate matter emissions are increased by ethane and propane, but are virtually eliminated by including nitrogen or hydrogen in the fuel

The effects of fuel dilution in a natural-gas direct-injection engine

This study reports the effects of fuelling a heavy-duty single-cylinder research engine with pilot-ignited late-cycle direct-injected natural gas diluted with 0, 20, and 40 per cent nitrogen. The combustion duration is unaffected while its intensity is reduced and its stability is increased. Emissions of nitrogen oxides, particulate matter, hydrocarbons, and carbon monoxide are all reduced, with no effect on the engine’s performance and efficiency. The results indicate the benefits of increased in-cylinder turbulence and are of particular relevance when considering fuel composition variations with non-conventional sources of gaseous fuels

Load transient between conventional diesel operation and low-temperature combustion

The operation of diesel low-temperature combustion engines is currently limited to low-load and medium-load conditions. Mode transitions between diesel low-temperature combustion and conventional diesel operation and between conventional diesel operation and diesel low-temperature combustion are therefore necessary to meet typical legislated driving-cycle load requirements, e.g. those of the New European Driving Cycle. Owing to the markedly different response timescales of the engine’s turbocharger, exhaust gas recirculation and fuelling systems, these combustion mode transitions are typically characterised by increased pollutant emissions. In the present paper, the transition from conventional diesel operation to diesel low-temperature combustion in a decreasing-load transient is considered. The results of an experimental study on a 0.51 l single-cylinder high-speed diesel engine are reported in a series of steady-state ‘pseudo-transient’ operating conditions, each pseudo-transient test point being representative of an individual cycle condition from within a mode transition as predicted by the combination of real-world transient test data (for fuelling and load) and one-dimensional transient simulations (for intake manifold pressure and exhaust gas recirculation rate). These test conditions are then established on the engine using independently controllable exhaust gas recirculation and boost systems. The results show for the first time that the intermediate cycle conditions encountered during combustion mode change driven by the load transient pose a significant operating challenge, particularly with respect to control of carbon monoxide, total hydrocarbon and smoke emissions. A split-fuel-injection strategy is found to be effective in mitigating the negative effects of the mode change on smoke emissions without significantly increasing oxides of nitrogen or decreasing fuel economy; however, unburned hydrocarbon emissions are increased. Additional experimental testing was also conducted at selected intermediate cycles to understand the sensitivity of key fuel injection parameters with the split-injection strategy on engine performance and emissions

Effects of fuel composition on high-pressure non-premixed natural gas combustion

The effects of adding ethane or nitrogen on the ignition and combustion of a non-premixed high-pressure methane-air jet have been investigated using fundamental studies in a shock tube and advanced computational modelling. The results are then used to interpret the performance of a pilot-ignited natural gas engine fuelled with similar fuels. The results show that the influence of the additives on the gaseous jet auto-ignition process is relatively small, but that they have a greater effect on the research engine, where both fuels have similar influences on the spatial relationship between the gaseous jet and the pilot flame

Experimental investigation of low temperature diesel combustion processes

The work presented in this article investigates the three distinct phases of low temperature diesel combustion (LTC). Diesel LTC followed a cool flame–negative temperature coefficient (NTC)–high temperature thermal reaction (main combustion) process. The in-cylinder parameters, such as the charge temperature, pressure, and composition, had noticeable influences on these combustion stages. The NTC was strongly temperature-dependent, with higher temperatures inducing both an earlier onset of NTC and a more rapid transition from NTC to the main combustion process. An increase in the intake charge temperature led to an earlier occurrence of NTC and a reduction in the heat released during the cool flame regime. A higher fuel injection pressure improved fuel mixing and enhanced the low temperature (pre-combustion) reactions, which in turn led to an earlier appearance of the cool flame regime and more heat release during this phase. This increased the charge temperature and led to earlier onset of the NTCregime.Ahigher exhaust gas recirculation (EGR) rate reduced the intake charge oxygen concentration and limited the low temperature reaction rates. This reduced the heat release rate during cool flame reaction phase, leading to a slower increase in charge temperature and a longer duration of the NTC regime. This increased the ignition delay for the main combustion event. The injection timing showed a less significant influence on the cool flame reaction rates and NTC phase compared to the other parameters. However, it had a significant influence on the main combustion heat release process in terms of phasing and peak heat release rate