Reference fuel composition

A method of making a deposit-forming reference fuel composition comprising:

• preparing a high sulfur base fuel composition in an amount greater than 50 weight % based on total weight % of the deposit-forming reference fuel composition, wherein the high sulfur base fuel composition comprises greater than or equal to 200 ppm sulfur based on total sulfur content of the base fuel composition;
• and
• adding to the base fuel composition:
• a) a reactive diolefin dopant and b) a reaction initiating peroxide having an active oxygen content greater than or equal to 2 weight % based on total oxygen content of the reaction initiating, and having a half-life temperature between 80° C. and 200° C.;
• wherein the reactive diolefin dopant and the reaction initiating peroxide are added in a concentration ratio of greater than 1:1.

A fuel composition comprising:

• a high sulfur base fuel composition in an amount greater than or equal to 200 ppm sulfur based upon total sulfur content of the base fuel composition;
• a reactive diolefin dopant comprising a cyclic diolefin;
• and
• a reaction initiating alkyl peroxide with an active oxygen content greater than or equal to 2 weight % based on total oxygen content of the reaction initiating peroxide and a half-life temperature of greater than or equal to 90° C.;
• the fuel composition having a concentration ratio of greater than 1:1 for the reactive diolefin dopant to the reaction initiating peroxide.