Interesting fact: direct-injection, four-stroke petrol engines of the kind used by Audi could dispense with the starter motor, meaning an end to being stranded by a flat battery. The petrol in such engines is delivered directly into the cylinder and ignited by a spark, so the engine could be fired from cold by a quick squirt-n-spark in any cylinder that happens to have stopped in what would have been the power stroke, if it were running. Obviously it’s a bit more technical than that, but the approach is apparently perfectly possible. Clearly it could dramatically cut fuel consumption in city vehicles, by allowing efficient and instant stop-start use of the engine. Could this swing the efficiency pendulum away from diesel and back to petrol? The diesel engine’s compression ignition nature means it doesn’t lend itself to the technique.