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

Hydrogen storage in liquid hydrogen carriers: recent activities and new trends

Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers

Investigating the feasibility of ammonia as a decarbonised energy vector for marine applications

The thesis details work conducted to analyse the feasibility of ammonia as a decarbonised energy vector for applications in the marine sector. Ammonia is now gathering significant interest due to being a zero carbon energy vector potentially produced from water, air and renewable energy. To understand the viability of ammonia, a review of competing energy vectors such as hydrogen and methanol was conducted with the relative strengths and weakness assessed. The key challenges with ammonia were deemed to be with its safety and could be overcome by proper education and control of fuel handling. Following this, extensive reviews were carried out on the various production, storage and energy conversion technologies that enable the use of ammonia as energy vector. The review of the application of ammonia in internal combustion engines revealed a lack of prior scientific work related to the use of high energy combustion systems (plasma/radical initiated) in Internal combustion (IC) engines for improving combustion of ammonia. Pre-chamber Jet ignition (JI) is one such solution where a small amount of fuel is combusted in a pre-chamber producing a jet of reactive products that are distributed in the main-chamber and initiate the combustion at multiple sites in the main-chamber. The distributed ignition of JI enables it to achieve fast burn rates with shorter flame travel and short burn duration. Since ammonia suffers low laminar flame speed, there was a synergy to use JI to overcome this challenge. As a result, this became the primary focus of this work, particularly in the backdrop of several marine engine manufacturers recently proposing the use of ammonia in large MW scale engines without sufficient evidence of feasibility in the public domain. To evaluate the viability of JI as potential combustion system for ammonia powered IC engines, a single cylinder gasoline direct injection engine was upgraded to incorporate a port fuel ammonia injection system. With the engine capable of operating in spark ignition (SI), passive and active jet ignition, tests were initially conducted with spark ignition system to act as benchmark for the tests with JI systems. However, initial commissioning tests conducted with the aim of understanding the maximum viable substitution of ammonia in the engine and identifying the limitations of the test cell revealed several challenges that needed to be resolved before benchmarking tests could be carried out. While the hardware could operate on pure ammonia for engine speeds between 1000 and 1800rpm at a load of 12bar IMEPn (Net Indicated Mean Effective Pressure), increasing the speed or reducing the load degraded the combustion, requiring increase in the amount of gasoline (pump grade E10) co-fuelling to avoid misfires. Furthermore, higher load tests were limited by the ammonia flow rate the supply line could deliver. To help overcome these challenges, the geometric compression ratio of the engine was upgraded from 11.33 to 12.39 via a piston swap along with new camshafts which improved the effective compression ratio from 10.3 to 12.02 for the same valve overlap conditions. With these upgrades it was possible to operate the engine in pure ammonia at lower loads in a fully warmed up state. A test region was mapped with this iii | P a g e configuration to act as benchmark for the jet ignition tests, the results show that pure ammonia operation prefers low speed operation achieving 100% substitution at loads as low as 6bar IMEPn which increases to 9bar IMEPn at 1800rpm. When it comes to efficiency and emissions, pure ammonia operation achieved similar or slightly higher efficiencies by virtue of its favourable anti-knocking characteristics, while all carbon emissions and NOx decreased considerably compared to pure E10 operation. The tests conducted with the passive jet ignition systems were less favourable, with the engine unable to operate on pure ammonia in any of the test points selected for benchmarking. The results show the increase in flame development phase of the combustion which along with the inability to advance the spark results in poor substitution for ammonia. However, for similar substitutions, jet ignition systems offer better efficiency and emissions, indicating the potential of the systems provided the challenges with combustion inside the pre-chamber can be overcome (associated with non-optimised geometry for the ammonia fuel possessing relatively high quench distance and a critical topic for future work)

Investigating the feasibility of ammonia as a decarbonised energy vector for marine applications

The thesis details work conducted to analyse the feasibility of ammonia as a decarbonised energy vector for applications in the marine sector. Ammonia is now gathering significant interest due to being a zero carbon energy vector potentially produced from water, air and renewable energy. To understand the viability of ammonia, a review of competing energy vectors such as hydrogen and methanol was conducted with the relative strengths and weakness assessed. The key challenges with ammonia were deemed to be with its safety and could be overcome by proper education and control of fuel handling. Following this, extensive reviews were carried out on the various production, storage and energy conversion technologies that enable the use of ammonia as energy vector. The review of the application of ammonia in internal combustion engines revealed a lack of prior scientific work related to the use of high energy combustion systems (plasma/radical initiated) in Internal combustion (IC) engines for improving combustion of ammonia. Pre-chamber Jet ignition (JI) is one such solution where a small amount of fuel is combusted in a pre-chamber producing a jet of reactive products that are distributed in the main-chamber and initiate the combustion at multiple sites in the main-chamber. The distributed ignition of JI enables it to achieve fast burn rates with shorter flame travel and short burn duration. Since ammonia suffers low laminar flame speed, there was a synergy to use JI to overcome this challenge. As a result, this became the primary focus of this work, particularly in the backdrop of several marine engine manufacturers recently proposing the use of ammonia in large MW scale engines without sufficient evidence of feasibility in the public domain. To evaluate the viability of JI as potential combustion system for ammonia powered IC engines, a single cylinder gasoline direct injection engine was upgraded to incorporate a port fuel ammonia injection system. With the engine capable of operating in spark ignition (SI), passive and active jet ignition, tests were initially conducted with spark ignition system to act as benchmark for the tests with JI systems. However, initial commissioning tests conducted with the aim of understanding the maximum viable substitution of ammonia in the engine and identifying the limitations of the test cell revealed several challenges that needed to be resolved before benchmarking tests could be carried out. While the hardware could operate on pure ammonia for engine speeds between 1000 and 1800rpm at a load of 12bar IMEPn (Net Indicated Mean Effective Pressure), increasing the speed or reducing the load degraded the combustion, requiring increase in the amount of gasoline (pump grade E10) co-fuelling to avoid misfires. Furthermore, higher load tests were limited by the ammonia flow rate the supply line could deliver. To help overcome these challenges, the geometric compression ratio of the engine was upgraded from 11.33 to 12.39 via a piston swap along with new camshafts which improved the effective compression ratio from 10.3 to 12.02 for the same valve overlap conditions. With these upgrades it was possible to operate the engine in pure ammonia at lower loads in a fully warmed up state. A test region was mapped with this iii | P a g e configuration to act as benchmark for the jet ignition tests, the results show that pure ammonia operation prefers low speed operation achieving 100% substitution at loads as low as 6bar IMEPn which increases to 9bar IMEPn at 1800rpm. When it comes to efficiency and emissions, pure ammonia operation achieved similar or slightly higher efficiencies by virtue of its favourable anti-knocking characteristics, while all carbon emissions and NOx decreased considerably compared to pure E10 operation. The tests conducted with the passive jet ignition systems were less favourable, with the engine unable to operate on pure ammonia in any of the test points selected for benchmarking. The results show the increase in flame development phase of the combustion which along with the inability to advance the spark results in poor substitution for ammonia. However, for similar substitutions, jet ignition systems offer better efficiency and emissions, indicating the potential of the systems provided the challenges with combustion inside the pre-chamber can be overcome (associated with non-optimised geometry for the ammonia fuel possessing relatively high quench distance and a critical topic for future work)

Experimental Comparison of Spark and Jet Ignition Engine Operation with Ammonia/Hydrogen Co-Fuelling

Ammonia (NH3) is emerging as a potential fuel for longer range decarbonised heavy transport, predominantly due to 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 always be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine was upgraded to include gaseous ammonia and hydrogen port injection fueling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted under 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. It was found possible to run the engine on pure ammonia at low engine speeds at low to moderate engine loads in a fully warmed up state. When progressively dropping down below this threshold load limit, an increasing amount of hydrogen co-fueling was required to avoid unstable combustion. All metrics of combustion, efficiency and emissions tend to improve when moving upwards from the threshold load line. A maximum net indicated efficiency of 40% was achieved at 1800rpm 16bar IMEPn, with efficiency tending to increase with speed and load. Furthermore, comparing spark ignition with active and passive jet ignition (with the former involving direct injection of hydrogen into the pre-chamber only and the main chamber port fueled with ammonia), at different loads it was found that active systems can significantly improve early burn phase and reduce engine-out NOx compared to passive jet ignition and SI. While both Jet ignition systems required supplementary hydrogen, it accounted for ~1% (active) of the total fuel energy at high loads increasing with reduction in engine load