In a time when small and micro energy sources are becoming increasingly important
due to current environmental challenges, the efficient recovery of low-grade
waste heat has emerged as a key strategy to enhance overall energy
sustainability. Although extensive research has been conducted on energy and
exergy distributions in large-scale internal combustion engines, experimental
studies focusing on small, air-cooled gasoline engines remain limited,
particularly regarding the quantification of their recoverable energy potential.
Addressing this gap, this work analyzes and quantifies the global energy
distribution and exergy availability in a single-cylinder, spark-ignition,
air-cooled Robin EY15 engine operating at rotational speeds between 1500 and
4600 min−1, and throttle valve openings from one-quarter to full. The
defined control volume includes the engine and the load system. The mass flows
analyzed are fuel flow (standard gasoline), intake air, exhaust gas (assumed as
air) and cooling air, while the energy flows are net power and miscellaneous
heat losses. It is found that the maximum net and exergy efficiencies of the
engine are 14.1% and 13%, respectively, at 2500 min−1 and full open
throttle. The major energy dissipation ways are the cooling air 24.3%–73.6% and
miscellaneous losses 9%–61% (percentage related to total energy flow provided by
the fuel). Based on exergy analysis, between 6%–9.7% and 22%–29.7%,
respectively, of that energy flows are transformable into mechanical work;
however, the exhaust gases has the higher potential, between 22.7% and 34.7%.
The rate of exergy destroyed ranges between 69.6% and 89.7%, meaning that the
maximum achievable efficiency would range from 10.3% up to 30.5% throughout the
tested engine speed–load conditions. These findings provide useful insights into
the low-grade heat recovery potential of small-scale combustion engines and
contribute new experimental data to the field of micro energy systems.
