Hydrogen Fumigation on HD Diesel Engine: An Experimental and Numerical Study

The currently reported work was concerned with experimental and numerical evaluation of the potential to partially replace diesel with hydrogen fuel, which continues to attract attention as an alternative longer-term fuel solution. The experimental work was involved with the fumigation of hydrogen on a single cylinder HD diesel engine under two real-world driving conditions at low and mid loads. Highest practical hydrogen substitution ratios could increase indicated efficiency by up to 4.6 and 2.4% while reducing CO2 emissions by 58 and 32% at low and mid loads, respectively. Soot and CO emissions were reduced as more hydrogen was supplied, particularly at low load. The numerical study was made by using two distinct phenomenological models being run in parallel. While, an in-depth evaluation of the unique dual fuel combustion was possible, the arising errors were largely associated with lack of dual fuel burning velocity data, which will remain a key barrier to dual-fuel simulation

A study of transient over-fuelling during heavy knock in an optical spark ignition engine

The work was concerned with improving understanding of the effects of transient over-fuelling during heavy knocking combustion in modern spark ignition engines. The single cylinder engine employed included full bore overhead optical access capable of withstanding unusually high incylinder pressures. Heavy knock was deliberately induced under moderate loads using inlet air heating and a primary reference fuel blend of reduced octane rating. High-speed chemiluminescence imaging and simultaneous in-cylinder pressure data measurement were used to evaluate the combustion events. Under normal operation the engine was operated under port fuel injection with a stoichiometric air-fuel mixture. Multiple centred auto-ignition events were regularly observed, with knock intensities of up to ~30bar. Additional excess fuel was then introduced directly into the end-gas in short transient bursts. As the mass of excess fuel was progressively increased a trade-off was apparent, with knock intensity first increasing by up to 65% before lower unburned gas temperatures suppressed knock under extremely rich conditions. This trade-off is not usually observed during conventional low intensity knock suppression via over-fuelling and has been associated with the competing effects of reducing auto-ignition delay time and charge cooling/ratio of specific heats. Overall, the results demonstrate the risks in employing excess fuel to suppress knock deep within a heavy knocking combustion regime (potentially including a Super-Knock regime)

Evaluation of intake charge hydrogen enrichment in a heavy-duty diesel engine

Concerns over CO2 emissions and global warming continue to enforce the transport sector to reduce the fuel consumption of heavy duty diesel goods vehicles as one major contributor of CO2. Such powertrain platforms look set to remain the dominant source of heavy duty vehicle propulsion for decades to come. The currently reported work was concerned with experimental evaluation of the potential to partially displace diesel with hydrogen fuel, which continues to attract attention as a potential longer term alternative fuel solution whether produced on-board or remotely via sustainable methods. The single cylinder engine adopted was of 2.0 litre capacity, with common rail diesel fuel injection and EGR typical of current production technology. The work involved fumigation of H2 into the engine intake system at engine loads typically visited under real world driving conditions. Highest practical hydrogen substitution ratios increased indicated efficiency by up to 4.6% at 6bar IMEPn and 2.4% at 12bar IMEPn. In 6bar IMEPn, CO2, CO and soot all reduced by 58%, 83% and 58% respectively while the corresponding reduction of these emissions in 12bar IMEPn, were 27%, 45% and 71% respectively toward diesel-only baseline. Under such conditions the use of a pre-injection prior to the main diesel injection was essential to control the heat release and pressure rise rates

A study of hydrous ethanol combustion in an optical central direct injection spark ignition engine

The aim of this experimental work was to improve understanding of the influence of hydrous ethanol on combustion in an engine demonstrating a tendency for biased flame migration towards the hotter exhaust walls as often reported for typical modern pent roof design IC engines. The work aimed to uncover the degree of residual water content that can be reasonably tolerated in terms of combustion characteristics in future ethanol SI engines (with the energy required to reduce water levels then potentially reduced). The experiments were performed in a single cylinder optical research engine equipped with a modern central direct injection combustion chamber and Bowditch type optical piston. Results were obtained under part-load engine operating conditions (selected to represent typical highway cruising conditions) with hydrous ethanol at 5%, 12% and 20% volume water. Baseline results were obtained using pure isooctane. High-speed cross-correlated particle image velocimetry was undertaken at 1500 rpm under motoring conditions with the intake plenum pressure set to 0.5 bar absolute. The horizontal imaging plane was fixed 10 mm below the combustion chamber “fire face”. Comparisons were made to CFD computations of the in-cylinder flow. Complimentary flame images were obtained via the “natural light” (chemiluminescence) technique over multiple engine cycles. The flame images revealed the tendency of an iso-octane fueled flame to migrate towards the exhaust side of the combustion chamber, with no complimentary bulk air motion apparent in this area in the horizontal imaging plane. The faster-burning ethanol offset this tendency of the flame to migrate towards the hotter exhaust walls. The fastest combustion rate occurred with pure ethanol, with higher water content (>5%) generally slowing down the flame speed rate to 10.64 m/s from 10.92 of ethanol and offsetting the flame speed/migration benefit (in good agreement with recent laminar burning velocity correlations for hydrous ethanol). When adding 20% water to ethanol the combustion rate was significantly slower (8.2 m/s) with a considerable increase in flame shape distortion as quantified by flame image shape factor values. The results demonstrate how the added water increases flame distortion and leads to higher flame centre displacement. Such flame centre displacement could potentially be offset in the future with a spark plug location biased further towards the intake side of the chamber (albeit sometimes practically constrained by the priorities given to intake valve sizing and local cooling jacket design). The results indicate that ethanol fuels offset such bias flame growth and allow residual water to be tolerated for an equivalent degree of biased flame migration. The implication is reduced fuel production energy and cost required to produce usable ethanol fuels

Cyclically resolved flame and flow imaging in an alcohol fuelled SI engine

The work was concerned with improving understanding of the interaction of the bulk in-cylinder flow with turbulent premixed flame propagation when using varied fuels including iso-octane, ethanol or butanol. The experiments were performed in a single cylinder research engine equipped with a modern central direct injection combustion chamber and Bowditch style optical piston. Results were obtained under typical part-load engine operating conditions. High speed cross-correlated particle image velocimetry was undertaken at 1500 rpm under motoring conditions with the plenum pressure set to 0.5 bar absolute, with the horizontal imaging plane fixed 10 mm below the combustion chamber “fireface”. Comparisons were made to CFD computations of the flow. Complementary flame images were then obtained via natural light (chemiluminescence) over multiple engine cycles. The flame images revealed the tendency of the flame to migrate towards the hotter exhaust side of the combustion chamber, with no complementary bulk air motion apparent in this area in the imaging plane. In terms of fuel effects, the addition of 16% butanol to iso-octane resulted in marginally faster combustion. Fastest combustion was observed with ethanol, in good agreement with laminar burning velocity correlations within the literature. The ethanol could be seen to offset the tendency of migration of the flame toward the exhaust walls under the fixed spark timing conditions. This exhaust migration phenomenon has been noted previously by others in optical pent-roofed engines but without both flow and flame imaging data being available. The results may imply that the spark plug should ideally be biased further towards the intake side of the chamber if the flame is to approach the intake and exhaust walls at similar times resulting in symmetrical flame propagation, reduced premature wall quenching and hence increase combustion stability and thermal efficiency. Such a layout is typically not preferred due to the priority given to the central fuel injector (and associated cooling jacket) location and maximizing the size of the inlet valves for improved volumetric efficiency

The Use of Active Jet Ignition to Overcome Traditional Challenges of Pre-Chamber Combustors Under Low Load Conditions

The need for advanced combustion technologies for use in future highly efficient powertrains in the automotive sector is well understood. Pre-chamber combustors, a technology with numerous historic examples, are fast becoming a major area of research once again. Pre-chambers are proportionally small partially enclosed chambers where combustion of a small quantity of fuel and air initiates before transferring to the main cylinder and, in spark ignition applications, subsequently igniting the bulk of the fuel and air. Pre-chambers effectively cascade two combustion events in order to increase the ignition energy present in the main combustion event, thereby enabling stable combustion of difficult-to-ignite main chamber mixtures, such as those with high levels of dilution. A traditional weakness of the subset of pre-chamber concepts known as jet igniters is poor low load engine performance. Combustion stability challenges and insufficient spark retard authority under heavily throttled conditions have limited the prospects of commercial implementation of jet ignition in modern engines. This study seeks to evaluate the root cause of these limitations and propose practical solutions that leverage the inherent flexibility of auxiliary fueled (active) jet ignition. Results of these experiments demonstrate the ability of a jet ignition engine to achieve idle and catalyst heating performance consistent with that of modern SI engines, thereby reducing the barriers to commercial implementation

Hydrogen and oxygen fuel enrichment effects on a HD diesel engine

Implementing emission regulations in the transport sector is enforcing manufacturers to improve performance of Heavy Duty (HD) vehicles as they are accountable for 25% of CO2 emissions within EU. The currently reported research was involved with evaluating partial replacement of hydrogen with diesel fuel experimentally and intake air enrichment with oxygen in a heavy-duty diesel single cylinder engine. Fumigation of hydrogen was done into the intake system at two particular engine loads (6 and 12 bar IMEPn). Indicated efficiency was increased up to 4.6% at 6 bar IMEPn and 2.4% at 12 bar IMEPn, while reducing CO2 emissions by 58% and 32% at 6 and 12 bar IMEPn respectively. Applying diesel pre-injection was required in order to mitigate the high pressure rise rates known as combustion noise. Furthermore, intake air enrichment with oxygen resulted in faster combustion process. This could curb soot and minimised CO emissions to the detriment of NOx increase

Assessing the Accuracy of Soot Nanoparticle Morphology Measurements Using Three- Dimensional Electron Tomography

Morphology plays an important role in determining behaviour and impact of soot nanoparticles, including effect on human health, atmospheric optical properties, contribution to engine wear, and role in marine ecology. However, its nanoscopic size has limited the ability to directly measure useful morphological parameters such as surface area and effective volume. Recently, 3D morphology characterization of soot nanoparticles via electron tomography has been the subject of several introductory studies. So-called '3D-TEM' has been posited as an improvement over traditional 2D-TEM characterization due to the elimination of the error-inducing information gap that exists between 3-dimensional soot structures and 2-dimensional TEM projections. Little follow-up work has been performed due to difficulties with developing methodologies into robust high-throughput techniques. Recent work by the authors has exhibited significant improvements in efficiency, though as yet due consideration has not been given to assessing fidelity of the technique. This is vital to confirm significant and tangible improvements in soot-characterization accuracy that will establish 3D-TEM as a legitimate tool. Synthetic ground-truth data was developed to closely mimic real soot structures and the 3D-TEM volume-reconstruction process. A variety of procedures were tested to assess the magnitude and nuances of deviations from ground-truth values. Results showed average Z-elongation due to the 'missing-wedge' at 3.5% for the previously developed optimized procedure. Mean deviations from ground-truth in volume and surface area were 2.0% and-0.1% respectively. Results indicate highly accurate 3D-reconstruction can be achieved with an optimized procedure that can bridge the gap to permit high-throughput 3D morphology characterization of soot

Research and innovation identified to decarbonise the maritime sector

The maritime sector requires technically, environmentally, socially, and economically informed pathways to decarbonise and eliminate all emissions harmful to the environment and health. This is extremely challenging and complex, and a wide range of technologies and solutions are currently being explored. However, it is important to assess the state-of-the-art and identify further research and innovation required to accelerate decarbonisation. The UK National Clean Maritime Research Hub have identified key priority areas to drive this process, with particular focus on marine fuels, power and propulsion, vessel efficiency, port operations and infrastructure, digitalisation, finance, regulation, and policy.This article was delivered by the UK National Clean Maritime Research Hub established on the 1st September 2023 supported by the UK Department for Transport (DfT) as part of the UK Shipping Office for Reducing Emissions (UK SHORE) Programme and Engineering and Physical Sciences Research Council (EPSRC) [grant number EP/Y024605/1]

Evaluation of Ammonia Co-fuelling in Modern Four Stroke Engines

Ammonia (NH3) is emerging as a promising alternative fuel for longer range decarbonised heavy transport, particularly in the marine sector due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine equipped with gasoline direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted under overall stoichiometric conditions with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance and engine-out emissions (including NH3 “slip”). With a geometric compression ratio of 12.4:1, it was possible to run the engine on pure ammonia at low engine speeds (1000-1800rpm) at low-to-moderate engine loads in a fully warmed up state. When progressively dropping down below a threshold load limit, an increasing amount of gasoline co-firing was required to avoid engine misfire. Due to the favourable anti-knock characteristics, pure ammonia operation was up to 5% more efficient than pure gasoline operation under stable operating regions. A maximum net indicated thermal efficiency of 40% was achieved, with efficiency tending to increase with speed and load. For the co-fuelling of gasoline and ammonia in a pure ammonia attainable operating region, it was found that addition of gasoline improved the combustion, but these improvements were not sufficient to translate into improved thermal efficiency. Emissions of NH3 slip reduced with increased gasoline co-fuelling, albeit with increased NOx. However, the reduction in NH3 slip was nearly 10 times the increase in NOx emissions. Comparing pure NH3 and pure gasoline operation, NOx reduced by ~60% when switching from pure gasoline to pure NH3 (as the latter is associated with longer and cooler combustion). Results were finally compared to those obtained a modern multi-cylinder Volvo “D8” turbo-diesel engine modified for dual fuel operation with ammonia port fuel injection, with the focus of the comparison being NH3 slip and NOx emissions