Effect of Cetane Number on Specific Fuel Consumption and Particulate Matter and Unburned Hydrocarbon Emissions from Diesel Engines

This paper discusses the effect of ignition delay time in diesel engines on the formation of particulate matter, using fuel formulations with different sulfur concentrations from various sources. Our findings indicate that the cetane number has a significant influence on particulate matter emissions, especially in engines with mechanical fuel injection. The maximum pressure in the combustion chamber increases as the cetane number increases, favoring the increase in the cracking reactions of high molecular weight fractions remaining in the liquid state and thus increasing the production of particulate matter. In certain conditions, this increase in pressure has a beneficial effect on the thermal efficiency of the cycle. Higher temperatures in the combustion chamber augment the speed of oxidation, reducing unburned hydrocarbon emissions. The ignition delay time of fuel has a strong effect on the formation of particulate matter and on the emission of unburned hydrocarbons. 1. Introduction Cetane number (CN) is an empirical parameter associated with the ignition delay time of diesel fuels, which is determined by means of standard tests based on the ASTM D613 standard [1]. Ignition delay is the time interval between the start of fuel injection and the beginning of the oxidation reaction. Ignition delay period starts with the injection of fuel and consists of physical and chemical delay periods until the autoignition occurs [2]. Fuels with a high CN have a very short ignition delay time; that is, ignition occurs in a very brief interval of time after injection begins. Conversely, the longer the ignition delay time the lower the CN. The ignition delay time of diesel cycle engines is a fundamental parameter to effectively control the combustion process, allowing for high thermal efficiency through maximum pressures close to 15° after reaching the top dead center (TDC), with which the maximum torque characteristic of Diesel cycle engines is obtained [3]. The ignition delay time is influenced by several physicochemical phenomena associated with the nature of the fuel, such as molecular structure, volatility, viscosity, surface tension, and mechanical characteristics of the engines, such as compression ratio, pressure of the injection system, and injection angle [4]. Ignition delay time can be expressed in milliseconds or angle of injection after the TDC [5, 6]. Fuels containing high concentrations of n-paraffins generally have low ignition delay times since the activation energy to form free radicals and start the oxidation process is low compared to that of