No, diesel motorcycles do not have spark plugs. Unlike gasoline engines, which use spark plugs to ignite the air-fuel mixture, diesel engines operate on the principle of compression ignition.
In a diesel engine, air is drawn into the combustion chamber during the intake stroke. Then, the air is compressed to a high pressure and temperature during the compression stroke. At the top of the compression stroke, fuel is injected directly into the combustion chamber. The high temperature and pressure cause the fuel to ignite spontaneously, without the need for a spark plug.
Since diesel engines rely on compression ignition, they do not require spark plugs for the combustion process. Instead, they use glow plugs during cold starting to preheat the combustion chamber and aid in the ignition of the fuel. Glow plugs are electric heating devices that heat the air inside the combustion chamber to assist in achieving the necessary temperature for combustion, especially during cold weather conditions.
It's worth noting that while diesel motorcycles exist, they are relatively uncommon compared to gasoline-powered motorcycles, which are more prevalent in the market.