Original scientific paper Reliability and thermodynamic properties of reciprocating compressors are largely dependent on the valve. Since the valves open and close automatically, there is an intensive impact of the valve and the sealing element dynamics to the gas flow through the valve. Poor valve characteristics inevitably lead to degradation of compressor performance and/or short lifetime of the valve. A short lifetime of the valve is the result of excessive impact forces between the sealing element and other parts of the valve assembly. Matching the valves to the specific reciprocating compressor is a complex task that requires the use of appropriate mathematical models before the realization of the valve. The mathematical model for the prediction of the valve dynamics is presented within this paper. The mathematical model is verified by measurements of thermodynamic characteristics of the specific reciprocating compressor used in motor vehicles. It is concluded that the mathematical model agrees well with the results of laboratory tests. Keywords: reciprocating compressor; valve dynamics; valve flow Dinamika ventila stapnih kompresora za motorna vozilaIzvorni znanstveni članak Pouzdanost i termodinamička svojstva stapnih kompresora uvelike ovise o ventilu. Budući da se ventili otvaraju i zatvaraju automatski, postoji intenzivno djelovanje dinamike ventila i elementa za brtvljenje na protok plina kroz ventil. Loše karakteristike ventila neminovno dovode do degradacije rada kompresora i /ili kratkog vijeka trajanja ventila. Kratki vijek trajanja ventila rezultat je prekomjernih udarnih sila između elementa za brtvljenje i drugih dijelova sklopa ventila. Usklađivanje ventila sa specifičnim stapnim kompresorom složen je zadatak koji zahtijeva primjenu odgovarajućih matematičkih modela prije nego se ventil uskladi. U ovom radu predstavljamo matematički model za predviđanje dinamike ventila. Matematički model se provjerava mjerenjima termodinamičkih karakteristika specifičnog stapnog kompresora u motornom vozilu. Zaključeno je da se matematički model dobro slaže s rezultatima laboratorijskih ispitivanja.

Large Diesel and gas engines with power higher than approximately 1 MW play a major role in the sea and land transport of people and goods, but also in the production of electrical energy in remote areas, for peak load balancing, and backup systems. While their total installed power and fuel consumption are vastly smaller than with their road transport counterparts, the vehicles they propel (ships and trains) represent the most efficient freight transport modes in existence. It is thus their importance for the world economy that has been driving their development, resulting in these engines belonging to the group of the most efficient thermal machines available to the mankind. Presented in the paper is a survey of the current development state of the large Diesel and gas engines in terms of their thermodynamic performance, emission levels and the means for achieving them, and fuels used. Due to its indispensability for achieving the high performance of these engines, turbocharging is given a particular treatment in the paper. Based on the study of the contemporary literature, an attempt is made to identify main development trends in this area. With regard to the latter, special attention is devoted to the so-called dual-fuel engines (Diesel and gas), which appear to have enjoyed a rapid development in the last decade.