Liquefied petroleum gas (LPG) as a medium-term option in the transition to sustainable fuels and transport

Undoubtedly, the changes spark ignition engines (hereinafter SI engines, Otto engines) have undergone under the last 20–25 years has been due to pressure from emission standards and fuel economy requirements becoming ever stricter. These regulations have equally influenced the every stage (from 1st to 5th generation) of LPG technology development while looking back in retrospective. Increasing emphasis on liquefied petroleum gas (LPG) as a clean, relatively low in cost and abundant energy source to provide affordable fuel-efficient transportation, encourages the search for the optimum approach to management of fuel, air and combustion to achieve the best results in vehicle power, fuel efficiency and low gaseous waste products. The development undertaken since then is still a “work in progress” leading to the course of establishing the new systems, including those for Otto engines with direct gaseous fuel injection as well as direct liquid LPG injection.