In the present study, dual fuel mode is investigated in a single cylinder optical compression ignition (CI) research engine. Methane is injected in the intake manifold while the diesel is delivered via the standard injector directly into the engine. The aim is to study by non-intrusive diagnostics the effect of increasing methane concentration at constant injected diesel amount during the combustion evolution from start of combustion.
IR imaging is applied in cycle resolved mode. Three filters are adopted to detect from injection to combustion phase with high spatial and temporal resolution: OD1.45 (3-5.5 μm), band pass 3.3 μm (hydrocarbons) and band pass 4.2 μm (CO2).
Using the band pass IR imaging qualitative information about fuel-vapor distribution and ignition locations during low and high temperature combustion have been provided.
The detected combustion emission both in the visible and IR wavelength range is measured by the images and compared with the in-cylinder pressure measurements and the ROHR. It was observed that the ignition delay is not affected by the premixed charge of methane and the combustion duration increases adding higher amount of methane. The combustion occurs along the different jets of diesel fuel in the azimuthal and radial locations of chamber and increasing the methane amount the combustion evolution is more homogeneous. CO2 and C-H bond evolution is strongly related to the CH4 amount demonstrating that the gas fuel contributes to combustion later than in the diesel fuel mode and confirming the presence of methanic species at the exhaust.