There were several types of torpedo propulsion. Three main types in WW2 were electric, internal combustion, and steam (a.k.a. “wet heater”).

As a rule, electric torpedoes had the lowest performance, but were inexpensive to manufacture and left no wake to revel their approach. Examples were the German G7e, the USN Mark 18, and the Japanese Type 92.

Steam torpedoes used a fuel and an oxidizer to create combustion and heat, applied water to create steam, and passed the steam through some type of engine. They varied in terms of source of water (some had fresh water tanks within the torpedo, some used salt water taken in from the ocean), the fuel used (USN used alcohol, Japanese used kerosene, the German G7a used decalin), the oxidizer (some Japanese torpedoes used compressed oxygen, most other navies just used compressed air, although at least a couple of models used air enriched with additional oxygen), and the type of engine the steam was passed through (reciprocating pistons or turbines). In the case of reciprocating engines, the number of cylinders varied from two to eight.

The only internal combustion torpedo engines that come to mind are several British torpedoes that used the “burner cycle”, which was kind of like a diesel engine. As I recall, these ran on shale oil. There may have been other internal combustion examples, but I can’t think of them.

A typical 21” (533mm) steam torpedo produced upwards of 300hp to achieve its maximum speed, usually around 45 knots. Many also had lower power settings available to achieve longer range. The Japanese Type 93 had what was probably the most powerful engine in a WW2 production torpedo, producing over 500hp.

Aerial torpedoes usually produced about 150hp, good for about 40 knots. The major exception was the USN Mark 13, which produced only 98hp, good for about 33 knots.