Yes, but it uses more fuel in order to get up to that temperature faster does it not? Therefore producing more CO2 & soot faster, but possibly still (about) the same amount? I know it will heat up faster, but I'm wondering if it will use significantly less fuel in getting to that heat faster, in which case there is less soot/CO2/whatever. If it doesn't, then it doesn't matter how quickly you heat it up, you're going to get (about) the same amount of soot deposited until you are at the correct temperature.