Search Results

Work by Plee, Ahmad, and coworkers in the 1980s [1, 2, 3, 4 and 5] showed that for changes in intake air state, Diesel NOx, soot, soluble organic fraction, and HC emissions could be correlated using the stoichiometric flame temperature calculated at SOC or peak pressure conditions. In the present work, similar flame temperature correlations are obtained for emissions from three test engines; a 1.2L high speed direct injection (HSDI) Diesel, a 2.4L HSDI Diesel, and a 2.34 L single cylinder direct injection (DI) Diesel engine, the first of which was tested using four alternative fuels. Use of the flame temperature correlations presented may reduce the number of engine tests required to evaluate the effects of EGR on emissions of NOx, particulate, and HC, even when alternative fuels are used.

Most computational schemes and kinetic models for engine-out NOx emissions from Diesels are based on the Zeldovich or extended Zeldovich mechanism. However, at pressures typical of both the premixed and diffusion portions of the combustion process, the third-body reaction leading to the formation of N2O (O + N2 + M) becomes faster than the leading reaction in the Zeldovich mechanism (O + N2). As in gas turbines, particularly those involving lean-premixed combustor designs, NO formation in Diesels through the N2O mechanism can thus proceed more efficiently than through the traditional route. Decomposition of NO in the combustion products during the power stroke can also occur by both the reverse Zeldovich reactions and the second order step that produces N2O (2NO ® N2O + O). Based on these observations, a skeletal mechanism consisting of seven elementary reactions is used to develop a two-zone model for NOx emissions from direct injection (DI) Diesel engines.