Fuel Consumption

[Ericj20]

How can you tell what engine/booster will consume fuel at what rate. I haven't really been able to determine how to figure this out. I of course figure that the more thrust output it produces would mean faster fuel consumption, but is this always true, or does it depend specifically on the booster or engine itself?

[Sapphire]

First, I'm gonna move this to Gameplay Questions And Tutorials.

Anyhoo, you can get that by looking at the engine's ISP. It has values for in-atmosphere and in-vacuum. Engines with high ISP are the most efficient and use the least fuel, such as the LV-N atomic engine in a vacuum.

[AmpsterMan]

Well you need to get the fuel consumption rate for the engine which could be found here for the LV-30 You then divide the Amount of Fuel you have by the consumption rate and you get how long it will burn for.

As for the relationship between Thrust and Efficiency, generally higher thrust engines have lower efficiencies and vice-versa. The reason for this is because as the efficiency of an engine doubles, the energy requirements quadruple, but the thrust only raises linearly. A nice discussion on the topic can be found here if you are interested.

[Smidge204]

The rate of fuel consumption is not a very important metric for rocket engines, so it's not given. The thrust:fuel-rate varies because engine efficiency varies.

But you can calculate it if you really want!

Engine Power = Isp * (Fuel / Seconds) * 0.052

The 0.052 is a factor I arrived at empirically. In incorporates several constants like gravity (9.81) and unit conversions into a single number.

You get engine power and Isp from the info box you get when you hover over a part. For example, the LV-909 has a power of 50 and an Isp at sea level of 300.

Let's build a simple ship out of a Mk 1 command pod, FL-T100 fuel tank, and LV-909 engine. The FL-T100 has a total of 100 units of fuel (45 fuel and 55 oxidizer = 100 units total fuel mass - as of right now, there is no separate fuel and oxidizer tanks so you will always have the proper proportions available). We can plug these values in:

50 = 300 * (100/t) * 0.052

t = 31.2 seconds

So burning at full throttle, this rocket will burn for 31.2 seconds and use up all the fuel. Alternatively, you can plug in "1 second" for time and solve for the Fuel:

50 = 300 * (Fuel/1) * 0.052

Fuel = 3.21 Units/second

Note that Isp is different for in-atmosphere and for in-vacuum, and will actually change as you ascend. Keep this in mind.

=Smidge=