Impact of coolant temperature on the combustion characteristics and emissions of a stratified-charge direct-injection spark-ignition engine fueled with E30

•Ethanol-blended gasoline can exacerbate engine cold-start emissions.•Using an E30 gasoline, fuel-efficient lean stratified-charge SI operation was studied.•Low engine coolant temperature increases exhaust soot, CO and HC emissions.•Optical diagnostics reveal more wall wetting and sooting flames for cold-start operation.•Lower coolant temperature leads to larger cycle-to-cycle combustion variability.