Ziliang Zheng Graduate Research Assistant e-mail: zhengziliang@gmail.com Tamer Badawy Research Assistant e-mail: Eng.tam@gmail.com Naeim Henein Professor e-mail: henein@eng.wayne.edu Wayne State University, Detroit, MI 48202 Eric Sattler US Army RDECOM-TARDEC, Warren, MI 48092 e-mail: eric.r.sattler.civ@mail.mil Investigation of Physical and Chemical Delay Periods of Different Fuels in the Ignition Quality Tester This paper investigates the physical and chemical ignition delay (ID) periods in the con- stant volume combustion chamber of the Ignition Quality Tester (IQT). IQT was used to determine the derived cetane number (DCN) according to ASTM D6890-10a standards. The fuels tested were ultra low sulfur diesel (ULSD), jet propellant-8 (JP-8), and two syn- thetic fuels of Sasol IPK and F-T SPK (S-8). A comparison was made between the DCN and cetane number (CN) determined according to ASTM-D613 standards. Tests were conducted under steady state conditions at a constant pressure of 21 bars and various air temperatures ranging from 778 K to 848 K. The rate of heat release (RHR) was calculated from the measured pressure trace, and a detailed analysis of the RHR trace was made particularly for the auto-ignition process. Tests were conducted to determine the physical and chemical delay periods by comparing results obtained from two tests. In the first test, the fuel was injected into air according to ASTM standards. In the second test, the fuel was injected into nitrogen. The point at which the two resultant pressure traces separated was considered to be the end of the physical delay period. The effects of the charge tem- perature on the total ID as defined in ASTM D6890-10a standards, as well as on the physical and chemical delays, were determined. It was noticed that the physical delay represented a significant part of the total ID over all the air temperatures covered in this investigation. Arrhenius plots were developed to determine the apparent activation energy for each fuel using different IDs. The first was based on the total ID measured according to ASTM standards. The second was the chemical delay determined in this investigation. The activation energy calculated from the total ID showed higher values for lower CN fuels except Sasol IPK. The activation energy calculated from the chemical delay period showed consistency in the increase of the activation energy with the drop in CN including Sasol IPK. The difference between the two findings could be explained by examining the sensitivity of the physical delay period of different fuels to the change in air temperature. [DOI: 10.1115/1.4023607] 1 Introduction The auto-ignition of fuel-air mixtures in diesel engines has a strong impact on combustion, performance, fuel economy, and engine-out emissions. The auto-ignition process includes overlap- ping physical processes that lead to the formation of an auto- ignitable mixture and chemical reactions that start the combustion process. Many efforts have been made to determine the effect of fuel properties on each of these processes, particularly with the increased interest in the use of renewable fuels to reduce the de- pendence on petroleum crude. Also, alternative fuels derived from petroleum crude and synthetic fuels are being considered for use in military diesel engines [1]. The separation between the physical and chemical processes has been known to be difficult to ascertain in diesel engines in part because of the complexity of the combus- tion chamber geometry, which affects the fuel distribution, and the high turbulence in the charge that affects the processes of spray evaporation and mixing with the air [2,3]. This is not the case in constant volume vessels where the charge is quiescent before start of injection. Furthermore, in engines the compressed air properties vary during the auto-ignition process, which makes it difficult to determine the effect of the charge temperature and pressure on the ignition delay period. Many correlations between the ID period measured in engines and charge properties were developed considering the temperature and pressure at the start of injection [4,5]. Other correlations considered the arithmetic mean pressure and temperature [6] or the integrated mean values [2,7,8] during the ID period. Such problems are reduced in constant vol- ume vessels where the changes in the charge temperature and pressure during the ID period are much smaller than in engines. Other advantages of using constant volume vessels in the study of the auto-ignition process include the simplicity of the experimen- tal setup and the smaller amount of fuel required for the experi- ment as compared to the engine setup and operation. Furthermore, it is feasible to run the experiment in the constant volume vessel by injecting the fuel into nitrogen [4,9,10] in order to differentiate between the physical and chemical processes, which would be very difficult and expensive in engines. In a nitrogen environment, the chemical processes that occur are only the endothermic reactions. The major parameters that affect the ID of conventional fuels in diesel engines are mainly the air temperature, air pressure [2,4,10], and the fuel molecular structure [3]. It has been found that the ID has higher sensitivity to changes in air temperature than changes in air pressure [2,3]. Also, the sensitivity of the ID to changes in charge temperature and pressure increases with the drop in cetane number of the fuel [3]. Furthermore, the ignition Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 20, 2012; final manuscript received January 31, 2013; published online May 20, 2013. Assoc. Editor: Joseph Zelina. Journal of Engineering for Gas Turbines and Power JUNE 2013, Vol. 135 / 061501-1 Downloaded From: http://gasturbinespower.asmedigitalcollection.asme.org/ on 10/16/2013 Terms of Use: http://asme.org/terms