The Type 93 "Long Lance" was no diesel.

It used compressed oxygen in a "wet heater" arrangement, as Robert M already said.

"Wet heater" engines varied a lot in design. In the case of the Type 93, the oxygen was used to burn kerosene. This heat was used to make steam, which was then forced through a 2-cylinder reciprocating (piston) steam engine of Whitehead design. The bore was 142mm, the stroke was 180mm, for a total displacement of 5.7 liters. It could generate 520hp at 1,200 rpm, giving a speed of 48 knots for about 12-14 minutes. Lower power settings of course resulted in lower speeds over longer times and longer distances.

An experimental version was tested at 850hp, and speed increased to 56 knots.

To reduce the chance of internal explosion on start up, the engine initially ran on compressed air, but quickly transitioned to oxygen. There were four 13.5 liter compressed air tanks. One was used for initial startup, while the other three powered the steering system.

Some sources say the torpedo used "liquid oxygen", but this is in error. The Type 93 used compressed oxygen at about 3,200 psi. The oxygen tank was huge, at 980 liters, and the torpedo also carried 128 liters of kerosene and 67 liters of lube oil (data for Type 93 Mod 1 and Mod 2). The consumed kerosene was displaced by seawater as the torpedo ran.

The motor would leave a trail of bubbles. The exhaust would be mostly steam and CO2. Obviously, the steam would quickly condense and mix with sea water, becoming invisible. The CO2 bubbles, however, would leave a trail. As Robert M already pointed out, the absence of the large amount of nitrogen used in other nations torpedoes reduced this trail considerably.