Search Results

The physical process of particulate fouling in EGR coolers is analyzed in this paper. Various particulate-deposition mechanisms are discussed and an order of magnitude comparison suggests that thermophoresis is the dominant mechanism for the EGR cooler fouling. The EGR temperature at the cooler inlet, the soot particle concentration in EGR, and the EGR mass flow rate are found to be the parameters governing the EGR cooler fouling. The structure for the soot deposit buildup on the cooler wall is also discussed. It is found that the surface layer of the deposit governs the fouling factor. A comprehensive model for soot particle depositions is developed employing heat, mass, and momentum transfer theories for the particle-gas system. The fouling model developed in this study can predict the process of deterioration in the effectiveness. The predictions of EGR cooler fouling are compared with experimental data and good agreement is observed.

A new fuel injection strategy is proposed for DME engines. Under this strategy, a pre-injection up to 40% demand is conducted after intake valves closing. Due to high volatility of DME, a lean homogeneous mixture can be formed during the compression stroke. Near TDC, a pilot injection is conducted. Combined fuel mass for the pre-injection and pilot injection is under the lean combustion limit of DME. Thus, the mixture is enriched and combustion can take place only in the neighborhood of sprays of the pilot injection. The main injection is conducted after TDC. Because only about half of the demand needs to be injected and DME evaporates almost immediately, combustion duration for the main injection plus the unburnt fuel in the cylinder should not be long because a large portion of the fuel has been premixed with air. With a high EGR rate and proper timing for the main injection, low temperature combustion could be realized.