As usually, once in the year, an issue of Thermal Science scientific journal is again dedicated to the research in the field of energy efficiency in the field of transportation sector with special emphasis on thermal processes of internal combustion engines as the main factor in vehicle fuel consumption. As in the previous special issue of this journal devoted to internal combustion engines, also this time, according to the opinions of our reviewers (whose list is given at the end of this issue) we have chosen 31 papers from a large number (about 60) of submitted manuscripts on internal combustion engine problems. Unfortunately, a number of papers have not been accepted for publication because of their lack of scientific level, since they mainly have presented obtained experimental results without any original or new insights. Presented papers in this issue suggest that, despite the global crisis in the field of manufacturing industries and vehicle production, research in the area of internal combustion engines are still very actual and intense. Of course, the current world energetic situation, global warming and air pollution affect also the intensive research in the transport sector. Therefore, these problems are represented in the papers of this issue.