Natural gas (NG) is a dirty mix of gasses when it comes out of the well. It gets cleaned up a little and put into a pipeline for industrial and residential use. it is also the feedstock for the big liquefaction "trains" that convert it to liquefied natural gas (LNG). I have no practical knowledge of this process, but the liquefaction process must surely produce fairly pure LCH4, since all the other components of the NG except Helium have higher boiling points and are valuable byproducts. So here is the question:
Can commercial LNG be used directly in a methalox rocket engine (after densification), or does it require additional purification?
If commercial LNG can be used directly, then just anchoring an LNG carrier offshore of a launch facility will solve the LCH4 delivery and storage problem.
No. The ISP is unknown.
And anyways, an LNG carrier offshore of a launch facility DOES NOT solve the LCH4 delivery and storage problem.
How would it be delivered?
The liquification process doesn't really purify it; it is still full of ethane, propane, probably some butane, along with a bunch of other stuff in unknown quantities (and the amount of variability in the makeup is large and constantly changing).
Could you shove it in a propellant tank and try to light up an engine? Sure. Would the engine run in some fashion? Depends on the engine. Pressure fed ablative? Probably. Something high performance using regen cooling with low margins? Probably not.
But, as Jim pointed out, the Isp will be wildly variable which makes it unusable for most applications. It would probably be fine for something at the college rocket project level where you don't care about performance, but for "real" vehicles you would 1) need to know exactly what is in the LNG, and 2) have it's component makeup be very consistent and repeatable.
The liquification process doesn't really purify it; it is still full of ethane, propane, probably some butane, along with a bunch of other stuff in unknown quantities (and the amount of variability in the makeup is large and constantly changing).
Could you shove it in a propellant tank and try to light up an engine? Sure. Would the engine run in some fashion? Depends on the engine. Pressure fed ablative? Probably. Something high performance using regen cooling with low margins? Probably not.
But, as Jim pointed out, the Isp will be wildly variable which makes it unusable for most applications. It would probably be fine for something at the college rocket project level where you don't care about performance, but for "real" vehicles you would 1) need to know exactly what is in the LNG, and 2) have it's component makeup be very consistent and repeatable.
Thanks. So the short answer is
NO. I speculate that in high volume, if you need pure LCH
4 It will be cheaper overall to start with gaseous NG and run a specialized liquefaction plant rather than starting with LNG.