Air-cooled Wankel Rotary Engine for General Use (II)

Factors Influencing Power Performance (1)

Abstract

In factors influencing the power performances of an air- and charge-cooled Wankel rotary engine for general use, principal factors controlling the quantity of blow-by gases past the sealing devices out of the combustion chamber are 1) the clearance of gas seals, 2) the stiffness of gas seal springs, and 3) other design measures such as adopting the dual side seals for a single, appending a seal ring around the center hole of a rotor as described later.
Experimental and theoretical investigations were done on the relationship between these factors and the power performance or the volumetric efficiency of proto type engines. Summary of results is as follows: -
(1) In the statical measuring experiments of the quantity of escape gases, which were performed on condition that the rotor was stopped at the rotating position of 90 degree from the top dead center, the maximum quantity in escape gases per unit contact length of gas seals was the gases past the clearance of the apex seal, but the maximum absolute quatity in escape gases was the gases past the side seal clearance (Fig. 1, 2, 3).
(2) In firing states, however, the clearance δ_c between the corner seal and the rotor slot has the greatest effects upon the power output, followed by 1) the clearance δ_al, which is the size difference between the length of the apex seal and the width of a rotor housing, i. e. the distance between both side housings, and 2) the clearance δ_at between the apex seal and its slot (Fig. 6, 7). The effect of 1) the clearance δ_st between the side seal and its groove, and of 2) the butt celarance δ_sl between the side seal and the corner seal on the power output is negligibly small.
(3) The design measures such as 1) adopting double side seals for a single, 2) appending a seal ring, i. e. an annular cast iron ring loaded by an O-ring which also acts as a secondary seal, in addition to the side seal, are effective for improving the volumetric efficiency η_v, since these measures reduce the quantity of blow-by gases toward the rotor center hole.
However, in the high speed range of more than 4000rpm, such design measures can not be adopted as the loss of power output increases rapidly (Fig. 4, 5).
(4) The gas seal clearances, which exert the greatest influence on the power performances, have to be made as small as possible taking consideration of the mutual relationship between machining accuracy and its cost (Table. 1).
(5) Though neccessary primarily for an engine starting aid, the gas seal springs are little neccessary after starting, since they are normally actuated by the combustion gas pressure. The stiffness of gas seal springs, therefore, should be made adegately soft (Table. 1, 2).