To be fair, the ammonia engine is an obvious holdover from their hydrogen attempts (which make sense in the specific context of Japan*). If they have the tech and they're not outright scrapping it, they might as well spruik it in case it works out.
*So, Japan imports most of the energy their electrical grid comes from, largely in the form of LNG. If Japan wants to move away from fossil fuels, then that new energy source needs to come in some form; importing liquid hydrogen has seemed an obvious prospect for years now.
This is important because if Japan's future electrical grid will run on hydrogen anyway, then a BEV's energy chain will be (imported hydrogen)->electricity->battery->car, whereas a hydrogen FCEV will just be (imported hydrogen)->electricity->car. Thus, hydrogen stands to be more efficient than BEVs in the specific context of future Japanese logistics.
But where does ammonia come into this? Simple: Ammonia, being NH4, has been considered as a better method of transporting hydrogen instead of liquid hydrogen (hydrogen has great specific energy (energy-per-weight) but literally the worst energy density (energy-per-volume), and ammonia could fix that. If so, then a car engine that uses ammonia directly could be more efficient than a hydrogen engine that's fed from ammonia anyway.
*So, Japan imports most of the energy their electrical grid comes from, largely in the form of LNG. If Japan wants to move away from fossil fuels, then that new energy source needs to come in some form; importing liquid hydrogen has seemed an obvious prospect for years now.
This is important because if Japan's future electrical grid will run on hydrogen anyway, then a BEV's energy chain will be (imported hydrogen)->electricity->battery->car, whereas a hydrogen FCEV will just be (imported hydrogen)->electricity->car. Thus, hydrogen stands to be more efficient than BEVs in the specific context of future Japanese logistics.
But where does ammonia come into this? Simple: Ammonia, being NH4, has been considered as a better method of transporting hydrogen instead of liquid hydrogen (hydrogen has great specific energy (energy-per-weight) but literally the worst energy density (energy-per-volume), and ammonia could fix that. If so, then a car engine that uses ammonia directly could be more efficient than a hydrogen engine that's fed from ammonia anyway.