@gwally's answer highlights the company Vector Launch Inc. and their Vector-R rocket, which uses three LP-1 18,300 lbf engines on the first stage and one LP-2 1,000 lbf second stage engine to put small payloads such as cubesats into LEO.
I think the "LP" in the engine names stands for liquid propylene, also called propene or C3H6 (one double bond).
What are some advantages to using propene over the more common and longer-chained kerosene such as RP-1? In what way would the design and operation of these L-propene/LOX engines be different than similarly-sized Kerolox engines?
With only three carbons, it's going to need to be cryogenic to be a liquid without extreme pressure, but not as cold as methane. I also wonder why liquid propene was selected over liquid propane, or other short hydrocarbons.
above: Images from here, here, and here.
above: Vector-R's three 1st stage LP-1 engines, from Spaceflight Insider.