October 2020

Other considerations Let’s not forget, if we consider hydrogen fuel cell stack electric power generation to be the future of transport, and bypass the significant issues in creating additional production capacity for pure hydrogen let alone the increase on electricity demand or environmental impact, there is a further important factor to consider. Fuel cell stacks like to generate power under steady state conditions. They do not like Vmax/ standing starts/traffic light GPs. So, we have electricity generated at a steady rate, but we have demands which are variable and include measured pollutants. The reason for Mazda doing this? The Wankel engine has two major drawbacks – sealing, and a long, thin combustion volume with a vast surface area to volume ratio. Yes, the Wankel engine is ‘emission disabled’. Meanwhile, BMW built a few factory-owned 7 Series E65 based long wheel base limousines, complete with CFRP body structure inserts around the rear sill/subframe/C pillar area. The V12 engine was fed with hydrogen stored in a large tank located in the boot above the rear subframe (hence the CFRP structural magic parts) and had a small fuel tank located under one rear passenger seat. The vehicle was bristling with contradictions – a huge engine which could run further on the tiny petrol tank that it could from the huge insulated hydrogen fuel tank, which was designed to keep the liquified fuel at -273°C for as long as possible. Oh, and it needed a system to ensure the liquid hydrogen became gas as it entered the pointlessly vast engine. These experiments confirmed what was already known before any of these prototype vehicles were built. Hydrogen does not have the energy density of petrol or diesel, and there are significant issues in storage of the fuel either at under pressure at normal temperature (i.e. serious pressure vessels) or super cooled at ambient (i.e. seriously bulky insulation). The second route? Drum roll…the hydrogen fuel cell. This is a form of battery. It has taken many years to develop, and the once sky-high cost of the main component – the ‘stack’ – is gracefully gliding downwards. Essentially pure hydrogen atoms are introduced to oxygen atoms, where a membrane allows the atoms to join and the electricity generated in the process is extracted. This is electric power generation from pure hydrogen and air, using the oxygen in the air. Hydrogen has a greater affinity to oxygen than oxygen has for hydrogen, so only one component needs to be made unstable to create the vital atomic level re-assembly. Do we need pure hydrogen to do this? Well Chrysler many years ago developed a fuel cell stack that would run on petrol or diesel, but of course the tail pipe emissions, while dramatically reduced, were higher than if we put pure hydrogen into the system. In addition, early membrane technology was highly intolerant of impurities, but much important work has taken place to make the fuel cell stack tougher. 26 AFTERMARKET OCTOBER 2020 TECHNICAL www.aftermarketonline.net