Research of Knocking Deterioration due to Accumulated Carbon Deposits on Piston Surfaces 2019-01-1141
In recent years, fuel economy regulation is expanding to reduce CO2 emission and energy saving in world wide. To achieve the regulation, automaker efforts to develop electrification technology and improve engine thermal efficiency with high compression ratio.
On the other hand, variety of fuels such as a reformed gasoline and bio fuel share is growing rapidly to utilize of fossil fuel by legal arrangements. With the spread of reformed gasoline, there are some risk of increased carbon deposit and accumulated on piston surface, due to heavy aromatic and olefin in the fuel. In combustion point of view, knocking should be deteriorated by synergy effect both accumulated carbon deposit and said high compression ratio. Furthermore, knocking deterioration do not occur in regularly, especially they occur in low-middle engine load. However, this mechanism is not clear.
To help resolve this issue, we investigate relationship between thermal effect for engine chamber temperature by accumulated carbon deposit and spark timing in low-middle engine load. As a results, knocking deterioration occur in specific spark timing angle. In this spark timing angle, reduction rate of combustion pressure increasing ratio (dP/dθ) by retard angle is a smaller than another spark timing angle.
Additionally, this paper describes the test to improve knocking deterioration with increased retard angle speed by knocking control system (KCS).Test results mentioned knocking deterioration period is reduced by 70%.