A conical rotary valve includes a conical valve body including a frustum of a cone and a first fluid passageway. The valve further includes a conical engagement body at least partially covering the conical valve body, where the conical engagement body comprising a second fluid passageway. The valve includes a valve actuator rotatably engaged to the conical valve body to provide a variable flow area that includes an intersecting area of the first fluid passageway and the second fluid passageway. The first fluid passageway and the second fluid passageway are structured such that a value δAf/δθv is monotonically increasing, where Af is the variable flow area and θv is a rotational angle of the conical valve body.