George wrote:

Diesels never have spark plugs.

Spark-converted diesels do. This is a diesel engine burning natural or
other fuel gas. The mixture is so lean it withstands the typical diesel
heat of compression and doesn't ignite until sparked. Or they can leave
the oil injection system in place and inject a small amount as a pilot to
trigger combustion. In the latter case such engines are often designed to
be able to up the amount of liquid fuel injected to normal levels while the
gaseous fuel is turned off in which case it's known as a dual fuel engine.

Purists will maintain that if a spark ignition system replaces the fuel
injection system then it's no longer a diesel. The problem with that is
that words mean what the majority says they mean. I can say that a single
"D" power cell is never by itself a "battery" but it's a lost cause.

Further, the definition of diesel as being an engine using the heat of
compression for ignition has not always been the case either. There was a
time when folks thought "Diesel" (it was usually capitalized in those days)
referred to an compression-ignition engine using high pressure air for
injection. Engines using "solid injection" as came to be standard were
known as "oil engines." You'll see pictures of some early Diesel
locomotives which say on their sides, "OIL ELECTRIC LOCOMOTIVE." Gradually
it was recognized that Dr. Diesel's big innovation was compression
ignition, not how fuel injection was done (or even what was injected...his
first experiment used coal dust!). My point here is simply that the
definition has been and is flexible. With that in mind, yes, sometimes
diesels have spark plugs.