The mixt. formation and ignition takes place in the second chamber with the medium and outlet valves closed. For expelling the used load out of the second chamber the medium valve remains open for one stroke and the outlet for approximately two strokes. On the compression stroke, the aspirated air is moved from the first to the second chamber, and on the work stroke the ignited work mixt. in the second chamber is transferred to the first where it loses its tension. In the expelling stroke the used load is sent outwards via the medium valve and the outlet valve. ADVANTAGE - Improves scavenging of the compression chamber, reducing fuel consumption and noise load.