By Jesse Crosse
Apart from fuel cells, there’s a slow but growing trend towards developing hydrogen combustion engines. JCB has proven the concept of its hydrogen-fuelled combustion engine while Toyota is exploring the same area.
It has been tried in the past, of course, with port-injection petrol engines, but the poor volumetric efficiency of burning hydrogen gas in an engine designed for atomised liquid fuel meant vastly reduced specific power (bhp per litre) and greater emissions. Direct injection and high compression ratios in specially crafted combustion chambers have changed that, which is why JCB and Toyota are succeeding with the latest engine and electronic hardware.
That said, there are plenty of eminent engineers and scientists working in the field of sustainable energy who view batteries as a better solution for storing electricity than hydrogen. They point out that the process of sustainably generating electricity, then making hydrogen from it, then consuming energy to compress it and then yet more to deliver it to a vehicle is far less efficient than simply making electricity and storing it in a battery.
It may be possible to improve the energy equation in one leg of that process, though, by compressing the hydrogen as it’s produced through the use of high-differential electrolysis rather than a mechanical pump. Conventional electrolysers produce hydrogen at relatively low pressure, but the ‘high output pressure’ design (first tested by Honda in 2010) has since been used to fill the compressed hydrogen tanks of fuel cell cars at 300 bar. Now it’s capable of filling them at 700 bar, the pressure needed to achieve range with a hydrogen fuel cell on a par with that of conventional cars.
Apart from improving energy efficiency, there are operational benefits, too. In existing retail installations of hydrogen filling stations, 13% of the time spent on maintenance goes on mechanical compressors, an overhead that could be removed from the equation.
Interest in hydrogen as a domestic gas is increasing and trials in the UK are ongoing to assess the viability of diluting natural gas with 20 percent hydrogen. At COP 26, the government announced the Whitelee project near Glasgow, which will generate and store enough green hydrogen to power 225 buses from Glasgow to Edinburgh on a daily basis. The hydrogen will be generated by the Scottish Power Whitelee Windfarm and converted to hydrogen by what will be the UK’s largest electrolyser to date, produced by ITM Power.
Given that one of the major strengths of hydrogen is also to store energy generated off-peak by converting it to hydrogen, the Whitelee project should demonstrate an approach to sustainable energy that has been talked about for the past two decades but has so far needed a real incentive to become a viable reality. The pressing need for energy security today might just be it.
