Extending ethanol energy fractions in ethanol-diesel dual-fuel combustion through EGR, intake conditions, and injection strategies

Misfire and excessive maximum pressure rise rates (MPRR) typically limit the ethanol energy fraction (EEF) in ethanol–diesel dual-fuel combustion. To extend the allowable EEF while maintaining combustion stability and acceptable MPRR, experiments were conducted on a medium-duty engine (1.1 L/cylinder) operating in intake-fumigation dual-fuel mode with ethanol and diesel. Tests at 6, 10, and 15 bar gross indicated mean effective pressure (IMEPg) evaluated the effects of EGR, intake conditions, diesel injection timing, rail pressure, and injection strategy on combustion, emissions, and efficiency. At 10 and 15 bar IMEPg, operation was primarily constrained by excessive MPRR. Under baseline conditions, maximum EEF was limited to 51 % at 10 bar IMEPg and 39 % at 15 bar IMEPg. Increasing EGR from 14 % to 48 % at 10 bar IMEPg reduced peak heat release rates, lowering MPRR below 5 bar/deg and extending achievable EEF to 82 %. Intake temperature influenced combustion phasing and burn rates; reducing intake temperature from 350 K to 330 K decreased MPRR and widened the allowable EEF range. At 6 bar IMEPg, operation was limited by misfire rather than MPRR. Stable combustion could not be sustained above 87 % EEF because high ethanol fractions suppressed diesel cool-flame reactivity. Increasing intake pressure improved combustion quality by advancing combustion phasing and increasing in-cylinder temperatures. Diesel injection timing and rail pressure were varied to assess diesel reactivity under high-EGR, high-EEF conditions. Lower rail pressures favored advanced injection timings because richer spray plumes promoted stronger early-stage reactivity, whereas higher rail pressures benefited from later injection timings to avoid excessive spray overmixing before ignition.