We don't have a problem with auto-ignition because the compressions used are far too low for that to happen. Most engines are around 9.5 to 10:1 with a very few up around 12:1 but they're designed for zero or very low nitro. Auto diesels run at about 22:1 compression to get enough heat to ignite the spray of fuel into the combustion chamber. The only engines that rely on heating up an air/fuel mix (which a true diesel doesn't do) is our model "diesels" but they need ether in the fuel because ether auto-ignites very easily. The burning ether then ignites the kero which is the part of the fuel that gives the power. Their compressions are around 17:1 but you can't pin down a figure for them because the compression is variable.