Choosing an engine and fuel
The four engines side by side, what each burns and where that fuel comes from, when to move up from one to the next, and what the Voltaic Cell adds.
The problem#
Every machine in Enthalpy runs on FE, and four engines make it. They differ in what they burn, how fast they make power, and how much effort the fuel takes. Pick by the fuel you can actually produce, not by the output on the box, because an engine without fuel makes nothing.
The four engines compared#
| Engine | Base output | Burns | Where the fuel comes from | Base-tier lanes it runs |
|---|---|---|---|---|
 Caloric Engine | 40 FE/t | Anything a furnace burns | Coal, charcoal, logs, sawdust, kelp blocks: whatever you have | 2 |
 Igneous Engine | 80 FE/t | Lava | A lava lake, a pump or a tank, piped in | 4 |
 Ignition Engine | 100 FE/t | Oils and refined fuels | Slick Eels, seeds, fish and crops, through the Vortex Separator, Distiller and Reaction Vat | 5 |
 Kettle Engine | 80 FE/t | Steam | Water and lava in the Vortex Separator's fluid mode, piped across | 4 |
Every engine holds 20,000 FE and pushes it out of its Output faces, by default the front. The fluid engines hold 8,000 mB of fuel and burn it in small sips. An engine only burns while its buffer has room, so one with nowhere to send power stops using fuel.
How far a unit of fuel goes#
Output is how fast an engine makes power; the fuel's value is how long that lasts. At each engine's base output:
| Fuel | In | FE each | Lasts |
|---|---|---|---|
 Coal | Caloric | 60,000 FE | 75 s |
 Block of Coal | Caloric | 540,000 FE | 675 s |
| A bucket of lava | Igneous | 200,000 FE | 125 s |
| A bucket of crude oil | Ignition | 100,000 FE | 50 s |
| A bucket of gasoline | Ignition | 400,000 FE | 200 s |
| A bucket of steam | Kettle | 25,000 FE | 16 s |
A steam bucket looks poor beside the others, but steam is not carried in buckets. Water makes five times its volume in steam, so what matters is the supply you can build. Fuel chains works the whole comparison through, and the fuel tables list every fuel.
When to move up#
Stay on the Caloric Engine while#
- You are early, or every machine you run is small. One engine runs 2 base-tier lanes.
- You can feed it without thinking: a chest of coal, charcoal or sawdust and Auto-input. A log-sawing line makes its own fuel.
Move to the Igneous Engine when#
- You have lava on tap, from a lake you can pump or a tank you fill. It makes 2× the Caloric Engine's output, takes fuel by pipe, and nobody has to restock it.
- You want the simplest hands-off supply. The only job is keeping lava flowing.
Move to the Ignition Engine when#
- You already farm fish or crops. Oil Globs, seeds and fish all turn into fuel, and refined, they are worth up to 4× what the crude oil is.
- You want the most power from one block: it has the highest base output, 100 FE/t.
Move to the Kettle Engine when#
- You have water and a little lava, and no fish farm to feed an Ignition Engine. An Aquifer makes the water for nothing.
- You want a steady supply that needs no restocking. It does need a Vortex Separator beside it to make the steam, which draws power of its own.
You rarely replace one engine with another. Once a base is running, several engines of different kinds share a Voltaic Cell, and the engines you can fuel cheaply do most of the work.
Making any engine stronger#
Tier kits raise an engine's output and buffer and open two module slots each. Engines take two modules, and they trade against each other: 
Celerity Modules raise output at the cost of FE per unit of fuel, and 
Economizer Modules get more FE from every unit of fuel. Fuel is the scarce thing for a hand-fed Caloric Engine, so lean towards Economizers; output is the scarce thing when you have fuel to spare. Upgrading machines compares them.
Where the Voltaic Cell fits#
The Voltaic Cell stores 1,250,000 FE at the base tier, and moves up to 1,000 FE/t in and out. Put one between the engines and the machines and it does four things:
- Smooths the load. Machines run in bursts; the cell takes the surplus when they idle and gives it back when several run at once.
- Pools engines. Several engines can push into one cell, and the cell feeds everything downstream.
- Charges your gear. Anything that takes FE charges in its slot.
- Powers a room. With a Tesla module it needs no cable; see Wireless power.
A cell evens out supply; it does not create any. The average output of your engines still has to meet the average demand of your machines.
Pitfalls#
- The engine pushes only from Output faces. By default that is the front. If nothing is powered, check that the front touches a machine or that you have set another face to Output.
- An engine does not take power. You cannot feed one engine from another, or charge it from a cell.
- Machines running Charging. Supply is below demand. Add an engine or an Economizer; Troubleshooting explains it.
- Steam cannot be bucketed. A Kettle Engine needs a pipe from its source, so place the Vortex Separator beside it.
- A tank refuses the wrong fuel. A fluid engine only accepts fluids on its list, and each engine has its own list. Lava goes only to the Igneous Engine.