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The regulatory framework of pollutant emissions concerning non-road small internal combustion engines is becoming increasingly challenging. The upcoming scenario threatens to cut out small two-stroke engines because of the fuel short circuit occurring during transfer and exhaust ports overlap, causing the emission of unburned hydrocarbons and reducing engine efficiency. Despite this challenge, small two-stroke engines are unmatched in high power density applications in which weight and autonomy hinder the diffusion of electric technologies. The continuation of small two-stroke engines in the market will thus depend on the capability of mitigating fuel short circuit. From this perspective, some of the Authors found the low-pressure injection technology fulfilling the purpose at engine full load; however, in addition to system complexity and costs, a lack of mixture homogenization was noted at low load.

Two-stroke (2S) engines still play a key role in the global internal combustion engine (ICE) market when high power density, low production costs, and limited size and weight are required. However, they suffer from low efficiency and high levels of pollutant emissions, both linked to the short circuit of fuel and lubricating oil. Low- and high-pressure direct injection systems have proved to be effective in the reduction of fuel short circuiting, thus decreasing unburnt hydrocarbons and improving engine efficiency. However, the narrow time window available for fuel to be injected and homogenized with air, limited to few crank-angles, leads to insufficiently homogenized fuel-air mixtures and, as a consequence, to incomplete combustions. The use of prechambers can be a well-suited solution to avoid these issues.