Gas Flow Studies in Direct Injection Diesel Engines with Re-Entrant Combustion Chambers

Abstract

Gas flow inside the cylinders of motored direct injection diesel engines was investigated, using fixed and moving hot wire probes. Particular attention was paid to swirl transfer into the bowl as the piston approaches the end of the compression stroke and to the bowl flow pattern. The investigation covered two bowl types in current use, a toroidal design and a re-entrant shape found to give low emissions. Measurements were also made in a re-entrant chamber of simplified geometry to provide data for theoretical modeling of gas flow and combustion processes. It was shown that swirl rates in the re-entrant bowl are generally higher than in the open bowl and that squish effects are much more noticeable. Swirling air is slower to come into re-entrant chamber during the compression stroke and does not seem to penetrate effectively to outer recesses; although swirl is held inside the bowl for considerably longer during expansion, clearly a significant factor in the ability to give good performance at retarded injection timings. Disadvantages of ultraviolet oscillographs for recording anemometer signals are noted (limited frequency response and laborious data processing). An appendix contains mathematical procedures for correcting anemometer readings to account for gas temperature variations.