Abstract In Memoriam—In memory of Dr. Zbigniew Magonski, a talented electronic engineer and inventor, was born in Glubczyce, Poland in 1950 and passed away in Cracow, Poland in 2017. He received M.Sc. degree in Solid State Technology from the Technical University of Wrocław, Poland in 1973, and PhD degree from the AGH University of Science and Technology, Cracow, Poland in 2000. For 15 years, he was with the R&D Center for Hybrid Microelectronics, Cracow Poland. At that time, his interest was focused on hybrid A/D, D/A converters also on DC HV power converters. Later, for 28 years, he was with the Department of Electronics, AGH University of Science and Technology, Cracow, Poland. His research interests covered ceramic microfluidic systems, hydrocarbon combustors, and high-temperature solid oxide fuel cells. In 1994–1995, he was with Summit Technology, Massachusetts, involved in a project relating to HV supplying of excimer lasers. He was a member of IMAPS US Chapter, the author of 13 patents and almost 50 technical papers connected with electronic technology. He was a caring husband and father and a good friend of many of us. We will miss you, Zbyszek. This article presents a proposal of a thermal instrument intended for the evaluation of heat energy of fluid fuels. Two thermal devices the flow meter and the combustor are the basic components of the instrument. The meter maintains a constant temperature in the vicinity of the combustion zone. The amount of heat energy in the fuel is calculated as the ratio of the electric power change expressed in Watts to the change of fuel supply delivered to the combustor within a time period of 1 s. The method enables a direct evaluation of fuel energy expressed in Joules per unit of mass or volume. For some applications, the meter may be a good alternative for a bulky bomb calorimeter.