My parents both worked for Douglas and I was at the inaugural takeoff of the first DC-8 in Long Beach. Like many of the 707s (which had entered service a year earlier) most of the DC-8s used water injection (and were called "water burners") as a means of increasing thrust at takeoff and also to cool the turbine blades at high RPMs. The upshot was that some of the fuel went unburnt, leading to the black smoke exhaust trails. But fuel was very cheap then.

Here's a cool 1959 UAL promo film covering a DC-8 transcon flight. Takeoff is around 5:40 in. Note the cabin amenities, also the ethnic makeup of the pax and crew.