Optimization of the process of charge combustion in compression ignition engine with multi-stage injection of hydrocarbon fuel and fuel with biocomponents in the Common Rail system, determines the main directions of research work in the field of thermo-oxidative stability of biofuels and the development of the engine design including fuel injection system. Resistance to oxidation is one of the most important properties of biofuel comprising FAME due to their low stability, and therefore a high tendency to oxidize, the results of which are products threatening the proper functioning and durability of high-pressure fuel-injection systems of diesel engines. The paper presents the results of laboratory tests of summer base oil with the participation of 7% (V/V) RME aging processes (oxidation and thermo-oxidative stability). An important role in these processes plays a selection of high-quality washing and dispersing additive. Bibliografia [1] Jakóbiec J., Ocena produktów z oleju rzepakowego przeznaczonych na paliwa silnikowe; Wydawnictwo Instytutu Gospodarki Surowcami Mineralnymi i Energią, Polska Akademia Nauk, Kraków, 2006. [2] Mc Cornick R., Rateliff M., et al., Several factors affecting the stability of biodiesel in standard accelerated test, Fuel Processing Technology 88/2007. [3] Worldwide Fuel Charter; Fifth Edition, September, 2013. [4] Stanik W., Badania poliizobutylenobursztynoimidów w zakresie oceny użytkowej dodatków detergentowo-dyspergujących do paliw silnikowych; AGH, Praca doktorska 2014. [5] Ullmann J., Geduldig M., et al., Investigation into the Formation and Prevention of Internal Diesel Injector Deposits, SAE Paper 2008-01-0926, 2008. [6] Caprotti R., Bhatti N., et al., Deposit Control in Modern Diesel Fuel Injection Systems, SAE Paper 2010-01-2250, 2010. [7] Stumpp G., Ricco M., Common Rail An Attractive Fuel Injection System for Passenger Car DI Diesel Engines, SAE Paper 960870, 1996. [8] Caprotti R., Breakspear A., Injector Deposit Test For Modern Diesel Engines, 5th International Colloquium Fuels TAE Esslingen, 2005. [9] Caprotti R., Breakspear A., et al., Detergency Requirements of Future Diesel Injection Systems, SAE Paper 2005-01-3901, 2005. [10] Leedham A., Caprotti R., et al., Impact of Fuel Additives on Diesel Injector Deposits, SAE Paper 2004-01-2935, 2004. [11] Caprotti R., Breakspear A., et al., Beyond 2008: The Challenges for Diesel Detergency, 6th Fuels International Colloquium on fuel tae Esslingen, 2007. [12] Birgel A., Ladommatos N., et al., Investigations on Deposit Formation in the Holes of Diesel Injector Nozzles, SAE Paper 2011-01-1924, 2012.