New adiabatic flame temperature model for nitrogen oxide formation with comparison of diethyl ether and diesel fuel

A 0.93-liter single cylinder diesel research engine was designed and built along with appropriate instrumentation, and data acquisition and reduction capabilities. A study of the effect of operating parameters on NO_x and particulate emissions was completed. Two fuels, Diethyl ether (DEE) and Diesel, were tested over a variety of operating parameters including load, speed, intake temperature and pressure, and intake O₂ percentage. The effect of fuels containing oxygen on the formation of NO_x and particulate was also investigated. The extended Zeldovich mechanism was used to describe NO formation in the Diesel engine. Flame temperature correlations for log (NO_x) vs. 1/T_F produced a straight-line relationship. Using several different single flame temperatures, correlations for Diesel and DEE were compared to each other and to research done by others. A new characteristic flame temperature was defined for improved flame temperature correlations between Diesel and DEE. This characteristic flame temperature is derived from flame temperatures throughout the combustion process, weighted by the heat release rate. Two correlations were made with this new flame temperature—one assuming no mixing between products and reactants and another assuming continuous mixing of products and reactants. Results indicated that in the unmixed case, NO_x is dependent on flame temperatures and load. In the mixed case, NO_x is only dependent on flame temperatures. Both cases show no distinction between the two fuels indicating that NO_x formation is independent of fuel type and only dependent on flame temperatures. A simple model for predicting NO_x emissions was also investigated based on the mixed and unmixed cases. Particulate were measured using a mini-dilution tunnel for both fuels. Diesel fuel produced the typical NO_x-particulate trade-off curve characteristic for this fuel. DEE produced particulate mass levels less than 0.1 g/hp-hr, even at equivalence ratios as high as 0.9, and at conditions where NO_x emissions were in the range of 0.2 g/hp-hr. This means that DEE has significantly improved NO_x-particulate trade-off characteristics relative to Diesel fuel.