Johnson's Baby Oil (usual disclaimer) is used in model-making circles as basic smoke. It is simply dripped onto a warm electric element, usually energised from a 12VDC supply. Hornby model trains (usual disclaimer) used the system extensively in their proprietary models, so the cheapest way to do it is to dismantle a broken locomotive found on the secondhand market and recover the smoke unit. About £10GBP might be enough to obtain one.
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