Controlling mechanism of ignition enhancing and suppressing additives in premixed compression ignition

Abstract

Abstract

Controlling ignition timing in the homogeneous charge compression ignition (HCCI) of dimethyl ether (DME) by adding methanol and ozone has been studied in a motored engine. In the standard pressure profile analysis, reduction of the first stage (cool ignition) heat release with methanol addition and consequent retardation of the second stage (hot ignition) was confirmed. Composition analysis, conducted under moderate, single cool ignition conditions, exhibited liner reductions of fuel consumption and formaldehyde formation. These observations were well reproduced by the detailed chemical kinetic model of Curran et al. for DME. A simple formulation accounting for the retarding effect was established. In contrast, acceleration with ozone addition is caused by the increase of heat release in the cool ignition taking place at a lower temperature. The cool ignition composition analysis showed increases of fuel consumption that are remarkable in lower equivalence ratio. Inclusions of ozone decomposition forming O + O₂ into the model enabled good reproduction of these features. It was inferred that the early radical supply from ozone reduced the cool ignition onset temperature significantly, where a stable intermediate accumulates owing to slow decomposition, and that the resultant reduction of formaldehyde formation induced the longer chain duration.