the reason for this is deemed to be that the arrangement shown in fig7 a tends to introduce the secondary flow b into ths swirl chamber in a manner which merely splits the main swirl increases thermal loss and invites reduce combustion temperatures while the arrangement shown in fig7 b appears to induce an insufficient increase in the flow path between the swirl and combustion chamber and thus produces a mediocre result as compared with the arrangement shown in fig7 c on the other hand it is thought the arrangement shown in fig7 d due to its acute bend is such as to induce a substantial pressure loss which inhibits the desired assist in the swirling motion produced by the main transfer port further design parameters which have been found important when designing an engine of the nature of the present invention are the cross sectional area and the length of the auxiliary transfer port experiments have revealed that if the ratio of the cross sectional area of the auxiliary tranfer passage to the length of same viz s l is greater than 0 5 then as shown in fig1 and 11 both the amount of smoke and nox produced by the engine can be held a relatively low levels the reason for this phenomenon is that the amount of fuel which is permitted to reach the main combustion chamber varies as a function of the cross sectional area of the auxiliary transfer port accordingly it is impossible to overly increase the diameter of the auxiliary tranfer port without encountering the problem that too much of the injected fuel is permitted to pass through the auxiliary passage and reach.