DIESEL AND BIODIESEL MACRO-SPRAY CHARACTERISTICS

Sažetak Karakteristike ubrizgavanja i formiranja mlaza u prostoru izgaranja jedan su od najvažnijih čimbenika modernih dizelovih motora i imaju značajan utjecaj na efektivne parametre i emisije ispuha. U posljednjih nekoliko desetljeća, biodizelu se kao motornom gorivu sve više posvećuje posebna pažnja. Unatoč tome što ima slične fizičke osobine kao dizelsko gorivo, svejedno veća gustoća, viskoznost i površinski napon mogu ponekad prouzročiti anomalije u procesu ubrizgavanja, kao što su npr. dodir mlaza sa stijenkama komore izgaranja, loše miješanje sa zrakom (prevelike kapljice) i drugo. U radu su prikazani rezultati istraživanja fizičkih svojstava dizelskog i biodizelskog goriva glede karakteristika ubrizgavanja i mlaza goriva. Utjecaj fizičkih osobina goriva proučavan je uz pomoć fizičko-matematičkog modela, simuliranjem procesa ubrizgavanja u konvencionalnom sustavu. Model je bio razvijen na IEPOI - Inštitut za energetiko, procesno in okoljsko inženirstvo Fakulteta za strojništvo, Univerza v Mariboru, koda Bkin, provjeren eksperimentalno na uređaju i na motoru. U posebnom smo uređaju izmjerili makro karakteristike mlaza (domet, kut, oblik), dok je vremensko prodiranje mlaza u mirujući zrak praćeno visokobrzinskom kamerom (2500 snimaka/s). Uz pomoć 3D programa (AVL "Fire"), dopunjena za ova istraživanja na IEPOI, mogli smo pratiti procese u motoru i odrediti ostale parametre mlaza (promjer kapljice i njihovu distribuciju u aksijalnom prosjeku) u ovisnosti o vremenu i odrediti njihove integralne prosječne vrijednosti i usporediti ih s vrijednostima dobivenih eksperimentom. U radu su prikazani rezultati utjecaja fizičkih osobina goriva i radnih uvjeta na karakteristike ubrizgavanja i mlaza goriva.Abstract Characteristics of fuel injection and spray formation in the engine combustion chamber are most important factor of up-to-date diesel engines, influencing their effective performance parameters and exhaust emissions. During last few decades alternative automotive fuels, such as biodiesel have received salient attention. Even though it has similar physical properties as diesel fuel, higher density, viscosity and surface tension of biodiesel may have a dominant influence on the spray formation and sometimes cause spray anomalies - such as contact between fuel and combustion chamber, poor mixing with air (bigger fuel droplets) etc. Results of the investigation about the impact of the diesel and biodiesel fuel physical properties on the injection and spray characteristics are presented in the paper. Physical properties of both have been examined and used in the mathematical model of the conventional injection system. The model was derived in IEPO - Institute for Power, Process and Environmental Engineering Faculty of mechanical engineering, University Maribor, simulation code Bkin, and was verified by experiment carried out on the fuel injection system test bench and on the engine. In a special test chamber the macro-characteristics of the spray injected into motionless air at the atmospheric pressure and room temperature (spray penetration distance, angle, and spray shape) have been measured and spray images were recorded by the high-speed camera (2500 frames/s). Using 3D simulation program (AVL "Fire") and including for the purpose of these investigations a few new estimates, the injection process for both fuels have been simulated and compared with the results obtained by experiments. These results are presented and discussed in the paper