Mazda HR-X

The Mazda HR-X was the first hydrogen powered concept car produced by Mazda. The car was unveiled at the Tokyo Motor Show in 1991. The car seated four people in a plastic shell and was powered by a two rotor Wankel engine which propelled it to 81 mph. The hydrogen was stored in a cooled metal hydride tank and 3.32 kg provided a range of 120 mi. It was the first in a series of demonstration hydrogen internal combustion engine vehicles produced by Mazda.

Design and development
The Mazda HR-X was a small concept car developed by Mazda a their plant in Aki District, Hiroshima to showcase the use of hydrogen fuel as a possible environmentally friendly alternative for automotive transport. The cabin accommodated four people who entered via gull-wing doors. It was constructed of plastic and designed to be nearly completely recyclable. The car was 3850 mm long and 1700 mm wide, with a maximum height of 1450 mm. Weight was 1260 kg.

The car was powered by a two rotor Wankel engine that produced 100 hp mounted in the rear. The Wankel engine was chosen as it solved the backfiring problems that beset previous attempts to run hydrogen in combustion engines. 37 Nm3 (3.32 kg) of hydrogen was stored in a metal hydride tank that was refuelled by a single nozzle alongside water for cooling. The engine was connected to the wheels via a 4 speed automatic transmission, while a KERS-like system called Active Torque Control System (ACTS) was used to recover braking energy and reuse it to improve acceleration. The car was capable of a top speed of 81 mph and had a range of 120 mi.

Legacy
A single example of the HR-X was displayed at the Tokyo Motor Show in 1991 and then in New York in 1992. However, it was not ready for production and no more were produced. The car was superseded by the more conventional HR-X 2 a year later, the next in line of a number of Wankel-powered hydrogen-fuelled vehicles developed by Mazda. The lineage culminated in the RX-8 Hydrogen RE and Premacy Hydrogen RE Hybrid produced in small quantities in 2007.