Research Of Ignition And Knocking On Gasoline PPCI Engine Which Based On Additives

Gasoline PPCI combustion has the advantage of high-efficiency and low emissions, especially with high compression ratio engine, the efficiency can be future improved. But at the same time, in a high compression ration engine, gasoline PPCI may also suffer the following obstacles, such as bad ignition performance at light load, and high tendency of knocking in heavy load. The objects of this thesis are to improve the ignition performance and expand the load of gasoline PPCI combustion by adding fuel additives on a single cylinder diesel, whose compression ratio is 17:1.First, according to hydrocarbon fuel and additive oxidation mechanisms, we concluded some key radicals that could influence the ignition, then we choose DTBP as the cetanenumber improver; secondly, according to the anti-knocking mechanism of additive, together with fuel and additive decomposition mechanism, we concluded some key radicals that causes violent combustion, and then we chose anti-knocking additive—DMC. At last, after some simulation work, we found the effects of different DMC amount to ignition and knocking, and roughly confirmed the amount of DMC.In order to clearly study the effects of additives to gasoline PPCI, we used PRF(nheptane-isooctane) to represent gasoline, and mixed with composite-additives. The experiments indicated that fuel without additives showed bad performance in light load, we need to improve the air temperature to ensure the normal start-up of the engine, but with DTBP, we could easily start the engine in cold condition; but at the same time, the engine showed a tendency of knocking during heavy-load. In this article, the amount of DTBP should be 1% of mass ratio, less than this ratio, the engine couldn't start, but a little bit more may brought the ignition timing too early. When DMC was added to the fuel, it could reduce the knocking tendency in heavy load, effects were extremely obvious when the amount was up to 20%, the amount couldn't be higher because the fuel consumption restriction. At the same time, the addition of DMC could deteriorate the cold start of engine. When compositeadditives(1%DTBP-20%DMC) were added to the fuel, the engine showed good performance in both light load and heavy load. So here we proved that the compositeadditives has a good effect on gasoline PPCI combustion.In the article, we also conducted the mechanism research of additives, including sensitivity-study and path-study. Study showed that: additive DTBP exert its effects by decomposing and releasing OH·, which caused the fast and early ignition of the fuel; by the contrary, additive DMC has its effects by slowing down the decomposition and release OH· in the combustion process. Both DTBP and DMC keep the original combustion path of the fuel.