Abstract
As various measures are being taken worldwide to restrain global warming, the internal combustion engine is required to realize a significant reduction in carbon dioxide emission. In addition, regulations of hazardous exhaust emissions in the global market are expected to become even more stringent near future. Regarding the diesel engine, it is well known that premixed charge compression ignition (PCI) combustion is effective in achieving both high efficiency and clean emissions. However, PCI combustion is associated with difficulty in controlling ignition timing and combustion noise, and this limits its operable range only to light load condition. In order to apply PCI combustion under higher load conditions, many researchers have been studying partially-premixed compression ignition (partially-premixed CI) combustion with use of multi-stage split fuel injection. Partially-premixed CI combustion can be expected to improve thermal efficiency by reducing combustion duration with a raised degree of constant volume of combustion, while suppressing exhaust emissions to a low level. In this type of combustion, PCI combustion occurs in the initial heat release process, and diffusive combustion becomes dominant in the latter part of combustion. If the spatial distribution of spray can be appropriately controlled to avoid interference between the burned region formed by early stage injections and the subsequent spray, it should be effective in forming leaner mixture in the latter combustion period. In this study, we investigated a new concept of partially-premixed CI combustion in which the spatial distribution of fuel spray is controlled with a dual zone combustion chamber composed of upper and lower zones. The effectiveness of the newly established combustion concept was validated by means of numerical analyses and engine experiments using a single cylinder research engine.
