Previous hydrogen researchers have demonstrated the great potential of hydrogen as a zero-carbon fuel and its wider operational ability to directly replace the existing fossil-fuelled internal combustion engines (ICE). Hydrogen direct-injection technology can operate at stoichiometric combustion conditions, fully eliminating the intake backfire phenomena, which has the benefit of low airflow requirements and is a suitable solution for naturally aspirated ICE platforms. However, significant challenges must be addressed when operating an H2 ICE at or near stoichiometric. These include rapid pressure rise rate, high in-cylinder gas pressure and temperature and the consequential higher engine-out NOx emissions. This study provides a comprehensive experimental analysis of the effect of water injection on a light-duty H ₂ engine’s performance, efficiency, burn durations and NOx emission. The engine was modified to operate with hydrogen via a centrally-mounted direct H2 injector and an intake port-mounted water injection system. The study included water vapour measurements, NOx concentrations and other exhaust gases. The practical implications of these findings are significant. The results demonstrated that the NOx emissions were reduced by 79% when the water was injected at a rate of 5 kg/h at 10 bar IMEP and 2000 rpm. This reduction in emissions, coupled with the observed decrease in cylinder pressure and the rate of pressure rise, could substantially improve engine performance and efficiency. At higher load regions, the water injection extended the maximum engine load to 24 bar IMEP and increased the engine torque output by 10%. The maximum Indicated Thermal Efficiency (ITE) increased from 41% at 16.5 bar IMEP to 42.5% at 18 bar IMEP at a lower lambda, with a corresponding reduction in the intake-air-boost pressure requirement. Of particular note, the use of water injection decreased the engine-out NOx emissions under high-load conditions by more than 55%, even at richer AFR compared to pure hydrogen operation.

Adopting zero-carbon fuels, like hydrogen, can significantly reduce environmental harm and pave the way for a decarbonised trajectory with zero carbon emissions. The hydrogen internal combustion engine (ICE) technology has demonstrated its reliability and capacity to seamlessly integrate into the current ICE platform, originally designed for diesel and gasoline operation. The direct utilisation of pure hydrogen eradicates steady-state carbon dioxide and hydrocarbon emissions. It is important to highlight that efforts to comprehend and comprehensively tackle NO_x emissions are underway. A comprehensive study was carried out to assess the NO_x emissions for a hydrogen ICE with different injection modes from gasoline. The study involved varying the relative air-to-fuel ratio (AFR) from stoichiometric to the lean-burn limit in a boosted spark ignition (SI) engine fuelled with gasoline or hydrogen. A fast NO_x emissions analyser was employed to measure the instantaneous NO and NO₂ emissions in the engine exhaust. The study provides a detailed analysis of NO_x emissions, including steady-state averaged emissions, average crank angle domain NO_x distribution and emissions, in-cylinder pressure analysis, as well as time and cycle analyses of NO_x emissions’ temporal and cyclic variations. The primary discovery was that NO_x emissions are almost zero between lambda 2.75 and 3.7, and hydrogen produces 13.8% less NO_x emissions than gasoline at stoichiometric operation. Finally, the full NO_x time analysis revealed that the consistency of NO_x emissions is higher with hydrogen than with gasoline by using a novel approach by identifying the coefficient of variation of the NO_x emission of each cycle.

The automotive industry must mitigate climate change by reducing vehicle carbon emissions and promoting sustainable transportation through technical solutions and innovations. Biofuels are seen as a solution to reduce CO₂ emissions, but they may affect fuel performance and emissions. Second-generation biogasoline mixed with ethanol has proven that it can be introduced as a drop-in fuel with the same performance and tailpipe emissions at the same level as fossil fuels. However, particulate matter (PM) emissions are significantly higher than fossil fuels. This study aims to experimentally investigate the effect of port and direct fuel injections on the PM emissions in a boosted spark ignition (SI) engine fuelled by Euro 6 standard biofuel with a 99 octane number blended with 20% ethanol compared to a fossil fuel baseline. The single-cylinder SI engine was equipped with two fuel injectors, a direct injector and a port fuel injector, and operated with externally boosted air. The split injection ratio was adjusted from 100% direct injection (DI) to 100% port fuel injection (PFI) to investigate the combustion characteristics and particulate emissions (PM) at different engine loads and speeds. The results indicate that by changing 100% DI to 80% PFI, PM emissions numbers between particle sizes of 23 and 1000 nm were dropped by 96.56% at a low load operation of 4.6 bar IMEP for the 99 RON E20 biogasoline and by 84% for the 95 RON E10 fossil fuel while maintaining the same indicated thermal efficiency and a similar level of other emissions. However, at a higher load above 10 bar IMEP, it was found that full DI operation reduced particulate numbers (PN) by 64% and 38% for 99 RON E20 biogasoline and 95 RON E10 fossil fuel at 20 bar IMEP, respectively, and enabled more stable operation at 3000 rpm with higher load operation regions.

Recent development of hydrogen (H ₂ ) internal combustion engine (ICE) technologies has demonstrated that they produce zero CO ₂ and ultra-low NO _X emissions without aftertreatment. Therefore, H ₂ ICE is well suited as a sustainable zero-carbon thermal power unit towards the net-zero target in the future. Increasing the compression ratio (CR) in IC engines can improve the indicated thermal efficiency (ITE). However, in spark ignition (SI) engines using gasoline, the CR is typically limited to around 10:1 due to knocking combustion. Hydrogen, with its higher autoignition temperature and octane number, can be used with a higher CR. This study aims to experimentally assess hydrogen as a direct replacement for gasoline in highly boosted single-cylinder SI engines with different CRs by swapping engine pistons. Two sets of experimental testing have been conducted at various engine speeds. Starting from a lambda (λ) sweep test involved leaning out the combustion to reach the engine stability-operating limits. The second test involved conducting a load sweep test on every CR at various loads to get the engine’s maximum in-cylinder pressure limits. The results indicate that, under the synergistic restriction of the engine strength and the lean-burn limitation, there is a crucial trade-off between peak and maximum engine power with various CR. Specifically, a higher compression ratio (i.e. CR = 12.39) resulted in a 5% increase in ITE compared to CR = 9.27. However, the lower compression ratio increased the maximum engine torque by 3.50 bar of indicated mean effective Pressure (IMEP). In addition, although hydrogen can remain stable combustion across a broad range of lambda and operating loads, the NO _X emissions increased with CR, due to the higher combustion temperature. These findings provide valuable insight into hydrogen engine applications and improve the understanding of SI hydrogen engine’s performance and development.