Fuel compositions for controlling combustion in engines

A method for making a modified naphtha boiling range spark ignition engine fuel composition comprising:

• forming a modified naphtha boiling range composition by adding a modifier composition to a first naphtha boiling range composition, the modifier composition comprising one or more compounds different from n-paraffins and isoparaffins that include a straight chain n-propyl group,
• the first naphtha boiling range composition comprising paraffins, isoparaffins, naphthenes, and aromatics,
• the first naphtha boiling range composition having a T5 distillation point of 10° C. or more, a T95 distillation point of 193° C. or less, and a research octane number (RON) of at least 80,
• the modified naphtha boiling range composition comprising paraffins, isoparaffins, naphthenes, and aromatics, the modified naphtha boiling range composition having a T5 distillation point of 10° C. or more, a T95 distillation point of 193° C. or less, and a RON of 80 to 101, wherein:
• an ignition delay of the modified naphtha boiling range composition is greater than an ignition delay of the first naphtha boiling range composition by at least 1.0 milliseconds,
• and
• a combined wt % of n-paraffins and isoparaffins that include a straight-chain propyl group in the modified naphtha boiling range composition is less than (−1.273×RON+135.6) based on a total weight of the modified naphtha boiling range composition.

A naphtha boiling range spark ignition engine fuel composition having a T5 distillation point of 10° C. or more, a T95 distillation point of 193° C. or less, and a research octane number (RON) of about 80 to about 101, the fuel composition comprising paraffins, isoparaffins, naphthenes, and aromatics, the fuel composition further comprising a combined wt % of n-paraffins and isoparaffins that include a straight-chain propyl group that, based on the total weight of the fuel composition, is less than the value from Expression 1 for the corresponding RON value of the fuel composition, wherein

• Expression 1 has the form:
• C3+ wt % (straight-chain propyl in n-paraffin
• RON Range
• and isoparaffin)
• 88.3 <= RON <= 91.4
• C3+ wt % <411.1 − 4.290 × RON
• (wt % 32.3-19.0)
• 91.4 <= RON <= 96.4
• C3+ wt % <73.8 − 0.600 × RON
• (wt % 19.0-16.0)
• 96.4 <= RON <= 97.9
• C3+ wt % <350.2 − 3.467 × RON
• (wt % 16.0-10.8)
• 97.9 <= RON <= 99.5
• C3+ wt % <−32.00 + 0.4375 × RON
• (wt % 10.8-11.5)
• 99.5 <= RON <= 101.1
• C3+ wt % <167.0 − 1.563 × RON
• (wt % 11.5-9.0).