Abstract: An improved rocket engine combustion chamber design wherein a first or precombustion chamber having a first diameter is located intermediate to a propellant injector and a second or main combustion chamber having a second diameter which is larger than the first diameter. The combustion chamber extends radially outwardly from the first diameter to the second diameter suddenly at the intersection between the precombustion chamber and the main combustion chamber. Film cooling is provided by providing a stratified layer of low temperature fluid adjacent to the inner wall of the precombustion chamber and surrounding a primary inner core of high temperature gases. The sudden stepped expansion at the interface between the precombustion chamber and the main combustion chamber provides secondary recirculation mixing of the propellants and will complete combustion between the main hot gas core and the propellant film cooling layer.