Operating an engine system includes autoigniting a first fuel including a plurality of liquid fuels premixed with air, to trigger ignition of a direct-injected main fuel in a first engine cycle, and receiving data indicative of an undesired heat release of combustion of the first fuel. The undesired heat release may include an undesired heat release rate (HRR) modality such as a multistage combustion. Relative amounts of the plurality of the liquid fuels are varied and admitted to the cylinder in a second engine cycle, and the first fuel having the varied relative amounts autoignited to trigger ignition of the direct-injected main fuel in the second engine cycle. The undesired heat release can be limited in the second engine cycle based on the varied relative amounts of the liquid fuels. The first fuel may include a blend of dimethyl ether (DME), methanol (MeOH), and water. The direct-injected main fuel may include MeOH and water. Related apparatus and control logic is also disclosed.