Another main engine burn to put the spacecraft into a shorter orbit poses a risk to completing the science goals of the mission, mission scientists say. (sciencenews.org)
This lets engines burn a mixture of air and fuel that has a much higher proportion of air than normal — known as «lean burn». (newscientist.com)
Most Z engines burn at least some oil, so the first thing to check is the oil level and, if you're buying privately, quiz the owner. (evo.co.uk)