Abstract
Abstract
On-board partial oxidation of gasoline to produce reformer gas seems to be an attractive strategy to abate pollutant emissions from internal combustion engines. The engine behaviour in terms of efficiency and combustion process can be better understood by means of in-cylinder heat flux measurements. The study of the unsteady wall heat transfer, supported by previous studies of flame propagation and flame speed through ion sensors and optical fibres, reveals a limited influence of the reformer gas upon the heat transfer coefficient and possibly upon the flame-quenching distance, which is estimated in three different and independent ways.
A detailed statistical analysis of single-cycle heat flux shows that the cycle-to-cycle variation remains large when the fraction of reformer gas in the fuel blend increases, even if the global engine stability improves. The comparison of numerous data shows how the chemical energy is released partly within the flame and partly within the post-flame region. This last can account for as much as 30 per cent of the total energy release. The analysis of slow and fast-burning cycles with different fuel blends shows that this fraction of energy is released only when, during the expansion stroke, the cylinder temperature decreases below a certain threshold, allowing radicals to recombine and carbon monoxide (CO) completely to oxidize to CO 2 .
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