Optimization of combustion in micro combined heat and power (mCHP) system with the biomass-Stirling engine using SiO2 and Al2O3 nanofluids

•Electrical energy was produced from the biomass sources.•The highest efficiency was achieved when using sawdust biomass. The total efficiency varies between 9% and 30%.•A micro combined heat and power system has been studied with water-based nanofluids.•The results show that using Al2O3 and SiO2 nanofluids increases the thermal efficiency of the mCHP. In this paper, a typical mCHP system was integrated by gamma type Stirling engine to meet electric, heating and hot water demands. The combustion test results, which is a key technology for small and micro scale mCHP systems have been presented and the combustion parameters for the Gamma type Stirling engine power system are discussed. Finally, the effect of SiO2 and Al2O3 nanoparticles, dispersed in Polyalkylene glycol (PAG) of mCHP system on the viscosity and thermal conductivity, were investigated. Also, the effect of sawdust biomass fuel on mCHP system emissions (such as CO, NOx, HC) have investigated. The test results confirm the fact that Stirling engines that are driven by the temperature of biomass gases are able to achieve a valuable output power. Also, Analysis of pollutants showed that by increasing of sawdust mass flow rate from 0 to 0.14 (g/s), CO emissions increased 164 vol%, also HC and NOx emissions increased 295–24 ppm respectively. Finally, the comparison between Al2O3/PAG and SiO2/PAG nano-lubricant demonstrate that Al2O3/PAG have better performance, therefore, the findings suggest Al2O3/PAG with a volume concentration of 0.010% as an optimum and best performance nano-lubricant for mCHP system. On the basis of the experimental results, we conclude that using the SiO2 and Al2O3 nanofluids in mCHP system can be introduced as new way to improve the performance of mCHP.