Mixing-Controlled, Low Temperature Diesel Combustion with Pressure Modulated Multiple-Injection for HSDI Diesel Engine

This paper proposes a new mixing-controlled, low temperature combustion (LTC) approach for high-speed direct injection (HSDI) diesel engines. The purpose of this approach is to avoid the excessively high pressure-rise rate (PRR) of premixed, kinetics-controlled LTC and to enable the low nitrogen oxides (NOx) combustion to operate over the wide speed and load range of the engine. To address the soot/noise trade-off at high load LTC operating conditions, the pressure modulated multiple-injection coupled with swirl control was applied. This injection strategy enables the injection of high pressure (HP) main spray into the local high temperature region of the already burning low pressure (LP) pilot spray injected from the neighboring injection hole. By employing this injection strategy, the equivalence ratio (φ) distribution of mixture is drastically varied during main combustion processes. The experimental results showed that by combining LP close-pilot injection, HP main injection near top dead center (TDC), and moderate swirl, the mixing-controlled LTC successfully achieve low engine-out NOx and soot emissions even at 13.7 bar IMEP while retaining high efficiency and low PRR. Furthermore, the 3D-CFD analysis clarified that the rich mixture of broadband φ distribution is formed at the beginning of main combustion followed by rapid homogenization of the mixture occurring as combustion progresses.