EFFECT OF FUEL BLENDS ON POLLUTANT EMISSIONS IN FLAMES SAYANGDEV NAHA, ALEJANDRO M. BRIONES, AND SURESH K. AGGARWAL* Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois, USA Fuel blending represents a promising approach for reducing both NO x and particulate emissions from flames. This paper reports a fundamental investi- gation on the effects of blending hydrogen with different fuels (methane and n-heptane) on the structure and emission characteristics of counterflow nonpremixed and partially premixed flames (PPF). The emission behavior is characterized in terms of the concentrations and emission indices of various pollutant species as a function of hydrogen content in the blend. Results indicate that hydrogen blending has a much more favorable effect on emissions in heptane flames than in methane flames. With hydrogen addition in methane=hydrogen blends, the emission index of C 2 H 2 (which is an important soot precursor) is reduced, CO remains unchanged, and NO increases slightly. In heptane=hydrogen blends, however, emission indices of all three species (NO, C 2 H 2 , and CO) decrease significantly with hydrogen addition. The behavior is attributed to two factors. First, for the same strain rate, the addition of hydrogen decreases carbon content in the fuel, which reduces the amount of CO and C 2 H 2 formed. Because C 2 H 2 is the major source of CH that leads to the formation of prompt NO, and because prompt NO is the dominant contributor to total NO in heptane flames, hydrogen addition leads to a dramatic decrease in NO emission in these flames. Second, the addition of hydrogen changes combustion chemistry due to the higher Received 25 May 2004; accepted 27 July 2004. This research was supported by the National Science Foundation Combustion and Plasma Systems Program for which Drs. Farley Fisher and Thomas Chapman have been the program directors. Many fruitful discussions with Professor I. K. Puri are gratefully appreciated. *Address correspondence to ska@uic.edu Combust. Sci. andTech., 177: 183^220, 2005 Copyright #Taylor & Francis Inc. ISSN: 0010-2202 print/1563-521X online DOI: 10.1080=00102200590883822 183