Fiabilitate şi Durabilitate - Fiability & Durability Supplement No 1/ 2016 Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X 67 STUDY ON THE NITROGEN OXIDES EMISSIONS GENERATED BY THE DIRECT INJECTION DIESEL ENGINES RUNNING WITH BIODIESEL PhD. Doru COȘOFREȚ 1 , Dr. Gheorghe SAMOILESCU 2 , Dr. Octavian TĂRĂBUȚĂ 2 1 Military Technical Academy, Bucharest, Romania, doru.cosofret@anmb.ro 2 “Mircea cel Bătrân” Naval Academy, Constanta, Romania. Abstract: Currently, research results on the use of mixtures of biofuels with fossil fuels to power diesel engines are controversial in terms of reducing emissions of NO in the exhaust gases of diesel engines. This diversity on the results is due to possibly different type of biodiesel used, the type of engine on which the tests were carried out and the methods and conditions for obtaining these results. Therefore research on biodiesel mixed with diesel is still a matter of study. In this regard, we conducted a laboratory study on a 4-stroke diesel engine naturally aspirated, using different mixtures (10, 15, 20, 25, 30, 40 and 50%) of diesel with biodiesel made from rapeseed oil. The study results revealed that the NO emissions of the mixtures used are lower than the same emissions produced when the engine is powered with diesel. Also, the emissions of NO do not have a significant drop in the case of mixtures compared with the diesel fuel. Keywords: biodiesel, diesel, NO emissions. 1. Introduction Nitrogen oxides are those pollutants products of fossil fuel combustion that occur due to chemical reactions of nitrogen (within the fuel and the atmosphere) and oxygen at high combustion temperatures during the combustion of gases. These pollutants products pose a particular interest for the study because they "are considered the main culprits for petrochemical mist above the cities and acid rain (and thereby creating a higher acidity of the soil)" [1]. The transport sector is one of the leading suppliers of emissions of nitrogen oxides from the exhaust gases of the propulsion engines and diesel-generators (for shipping). To promote the use of renewable energy in the transport sector, EU imposed that 20% of biofuels to be mixed with fossil fuels until 2020 [2]. This has led to further research on the effects of biodiesel mixed with diesel on the exhaust emissions from the exhaust of diesel engines. The majority of studies reported in the literature showed that the use of biodiesel as fuel for engines led to an increase in emissions of NO as compared to the diesel engine supply [3, 4]. The reason for the increase in emissions of NO is the earlier initiating of the combustion process in the engine when fueled with biodiesel, due to increased advances of injection due to the physical properties of biodiesel that are higher than diesel ’s, such as viscosity, density, and the higher oxygen content of the biofuel composition [5]. Due to the increased advance of injection into the combustion chamber, a larger quantity of biodiesel is injected to diesel fuel and therefore the ignition occurs earlier, leading to higher combustion temperatures peaks relative to pure diesel. A smaller number of researchers have reported a reduction in emissions of NO when biodiesel is used as fuel [4, 6, 7, 8].