Thermodynamic Analysis of a Reciprocating Engine Operating Under Heat Exchange

A thermodynamic analysis is presented for a reciprocating engine operating under heat exchange instead of through a combustion process, with the purpose to evaluate if such solution can be justified in the light of the obtainable performances. As far as the cycle is concerned, the engine operates identically to a conventional one, but the system configuration departs unavoidably from conventional solutions for reasons mainly related to heat exchange processes (exchanged thermal power, problems related to wall temperature, etc.). Taking into account real cycles effects, both attainable efficiencies and specific powers are determined, with reference to the system characteristics. Attainable efficiencies present quite satisfactory results, while specific powers, related to exchanged thermal powers, on the contrary, show much lower values than those normally encountered for conventional engines. The heat exchange, being clearly the main problem, has been evaluated by means of suitable calculation models. Reference has then been made to a particular engine configuration to contain those problems related to heat transfer from wall to working fluid. For the present analysis the main interest was for the Otto cycle, but also Diesel and mixed cycles have been considered.

Possible applications can be found, besides typical utilizations of high temperature gas streams, also within the possibility of partial close cycle (only for the working fluid) or total close cycle (for both working and heating fluids) operation. Independently anyway upon any possible applications, the present analysis has the purpose to show characteristics and limits of such kinds of systems.