Real-time residual mass estimation with adaptive scaling

A method of controlling homogeneous charge compression ignition in an engine, the method comprising:

• determining an estimated residual mass for a combustion cycle based on measured engine parameters and an estimated residual mass for a previous combustion cycle, the estimated residual mass including an estimated amount of fuel remaining in an engine cylinder at an end of the combustion cycle;
• determining a first temperature value for the cylinder based only on a calculated combustion phasing for the combustion cycle, wherein the calculated combustion phasing is based on cylinder pressure data directly measured during the combustion cycle;
• estimating a second temperature value for the cylinder based on the estimated residual mass for the combustion cycle;
• determining an adaptive scaling factor based at least in part on a discrepancy between the first temperature value and the second temperature value, wherein the adaptive scaling factor is indicative of an error of the estimated residual mass for the combustion cycle;
• determining an estimated residual gas fraction based on the estimated residual mass;
• determining an adjusted residual gas fraction by multiplying the estimated residual gas fraction by the adaptive scaling factor;
• and
• controlling at least one engine control variable during a subsequent combustion cycle based on the adjusted residual gas fraction, wherein the at least one engine control variable includes at least one engine control variable selected from the group consisting of timing of intake valve opening, timing of intake valve closing, timing of exhaust valve opening, timing of exhaust valve closing, timing of fuel injection, and mass of fuel injected.