In the original Nègre air engine, one piston compresses air from the atmosphere to mix with the stored compressed air (which will cool drastically as it expands). This mixture drives the second piston, providing the actual engine power. MDIs engine works with constant torque, and the only way to change the torque to the wheels is to use a pulley transmission of constant variation, losing some efficiency.  When vehicle is stopped, MDIs engine had to be on and working, losing energy. In 2001–2004 MDI switched to a design similar to that described in Regusci's patents (see below), which date back to 1990.
It has been reported in 2008 that Indian car manufacturer Tata was looking at an MDI compressed-air engine as an option on its low priced Nano automobiles. Tata announced in 2009 that the compressed-air car was proving difficult to develop due to its low range and problems with low engine temperatures.