Australian scientists seem to have found the key.
Pulse combustion uses rapidly resonating sound waves to drive escaping unburnt fuel and heat backwards to be re-ignited. In doing so the fuel is nearly completely consumed and more heat produced. The new system has applications for industrial heat generation but could also be used on a smaller scale, perhaps ending up in a refrigerator near you. The theory and practice of pulse combustion has been around since the 18th century. The Nazis employed it to power the rocket motors on their V1 flying bombs.