Mazda's commercialization of the Miller-cycle engine, an invention dating back to the 1940s, got more Japanese media attention than any single advance in fuel conservation. The engine generates 1.5 times the torque of a traditional engine of the same displacement, while improving fuel efficiency 10 to 15{a9573bd3aa901309c1f5fce5b559a91687eda4f627635006bb3caa1474469022}. In the Miller cycle, the compression stroke is shortened to attain a small compression ratio with a large expansion ratio. The engine achieves both low compression ratios and high expansion ratios by delaying the close-timing of the intake valves. To compensate for the decreased amount of intake air, caused by the delay of the closing intake valves, a Lysholm compressor pushes a large volume of compressed air into the cylinder with a screw-type rotor mechanism. Mazda's KJ-ZEM Miller-cycle engine is a 24-valve V6 DOHC model with a bore of 80.3 mm, stroke of 74.2 mm, displacement of 2,254 cc, actual compression ratio of 8.0, maximum torque of 30.0 kg-m/3,500 rpm, power output of 220 ps/5,500 rpm, and high expansion ratio of 10. The Lysholm compressor sits in the V-bank between the cylinder blocks and is driven by a V-belt. Rotors take air in and compress it by a factor of two. A 1.5 X increase in air volume goes to the combustion chamber even if a portion returns to the inlet manifold because of the delayed closing of the inlet valves.
Hydrogen powered
Mazda employed a hydrogen rotary engine on its HR-X2 concept vehicle that contains several improvements compared to commercially available versions. Most interesting is the improved torque in the low-to-mid rpm range. Mazda
