Reciprocating internal combustion engine

A compression-ignition constant-volume constant-temperature two stage combustion reciprocating internal combustion engine comprising:

• a first combustion stage configured to occur at about constant-volume, wherein a quantity of a first heat addition is selected to ensure that a first combustion temperature during the first combustion stage does not exceed a threshold temperature at which NOx formation occurs;
• and
• a second combustion stage configured to occur at about a second combustion temperature that remains about constant during the second combustion stage, wherein the second combustion temperature is about equal to the first combustion temperature at an end of the first combustion stage, wherein a quantity and a rate of a second heat addition delivered to the engine during the second combustion stage are configured to ensure that the second combustion temperature of the second combustion stage remains about constant during the expansion stroke even as cylinder pressure decreases.

A method for operating a compression-ignition reciprocating internal combustion engine, the method comprising:

• injecting a first quantity of fuel into a cylinder of the engine during a compression stroke of the engine to produce a first compression-ignition combustion event while a reciprocating piston is at top dead center in the cylinder;
• and
• injecting a second quantity of fuel into the cylinder during an expansion stroke of the engine to produce a second combustion event while the reciprocating piston is descending from top dead center, wherein injecting the second quantity of fuel has a start and an end, wherein injecting the second quantity of fuel is configured to maintain a constant mean cylinder gas temperature between the start and the end of injecting the second quantity of fuel, wherein injecting the second quantity of fuel has an injection rate, and wherein the injection rate increases between the start and the end of injecting the second quantity of fuel to ensure that the mean cylinder gas temperature remains constant despite the reciprocating piston descending in the cylinder during the expansion stroke.