Combustion characteristics of some alternative fuels in ICE:: a detailed numerical study

Two major fuels commonly used in compression ignition (CI) and spark ignition (SI) enginesare diesel and gasoline. The reserve of diesel and gasoline is limited, however the combustion ofthese fuels giving rise to air pollution. This calls for the search for alternative fuels, preferablyrenewable fuels, and the development of more efficient and clean combustion technologies forinternal combustion engines. The thesis deals with direct numerical simulation (DNS) of thecombustion process in various alternative fuels under conditions relevant to SI engines and CIengines. The fuels considered are methane, hydrogen, and methanol. The internal structureand the propagation speed of methane/air flames and of hydrogen-enriched methane/air flamesare studied for a range of equivalence ratio and pressure conditions. The methods of flame-cone-angle and flame-area for determining the laminar flame speed of methane/air flames inthe Bunsen burner configuration are evaluated using DNS. For hydrogen-enriched methane/airflames, the correlation between the laminar flame speed and the hydrogen enrichment ratio isdetermined for a range of equivalence ratios, efforts being made to the mechanisms involvedin the peak laminar flame speed shifting towards fuel-rich mixtures. For the studies on meth-anol combustion the focus was on the combustion characteristics of methanol/n-heptane/airmixtures under dual-fuel CI engine relevant conditions. It was found that methanol combus-tion under dual-fuel conditions can occur in multiple modes: auto-ignition, premixed flamepropagation and diffusion flame, depending upon the injection strategies and the ambient pres-sure and the ambient temperature conditions. The effects of different operating conditions onthe modes of methanol/n-heptane dual-fuel combustion were identified.