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In these days, not only low exhaust emission but also carbon dioxide reduction is required to achieve carbon neutrality toward resolution of climate change. Though examination of electrification and decarbonized fuel is progressing, industrial machines have issues for high load factor and infrastructure development. Therefore, trends of off-road powertrain are expected to be diversified depending on usage environment or applications. As a result, in terms of diesel engines below 19 kW, it should be the best way for satisfying the social needs to develop new diesel engines which have high environmental performance by optimizing engine combustion. In the case of diesel engines below 19 kW, it is difficult for the engines to adopt the direct injection (DI) combustion system and the common rail system (CRS). The fuel spray of these small displacement engines by DI or CRS easily attaches the wall surface of combustion chamber due to the small bores and causes increasing fuel consumption.

Recently, EU StageV emissions regulations have been enforced in the European market since 2019, increasing environmental requirements for diesel engines. EU StageV has been tightened compared to EPA Tier4 regulation, which demand PM (Particulate Matter) reduction and added new PN (Particle Number) regulations. Until the previous regulation EU Stage IIIA, the power category of 19kW or more and less than 37 kW had adopted mechanical IDI (Indirect-Injection). This mechanical engine is characterized by compactness and lightweight because of simple structure. Therefore, this engine is appreciated by customer with easy installation. On the other hand, to achieve EU StageV, it is necessary to adopt the electronic direct injection common rail system with more precise fuel injection and advanced exhaust gas aftertreatment device.

Off-road engines are requested with limited space due to variety of end products, and it is also requested reasonable costs for the limited end products prices. For that purpose, several small off-road engines have to comply with emission legislations by only engine modifications. However, the additional engine control and devices (=High pressure direct injection, combustion chamber modification, electrical control, turbo charging control, etc.) must be expensive, and increasing the total engine costs and manpower for developments. These are very critical issues for long term possibility of same engine productions which cover to new legislations in each country. Thanks to drastic fuel condition improvement for passenger cars / trucks around the world, it would be aroused one of the best solution by DOC (Diesel Oxidation Catalyst) systems rather than the engine modifications.