In a diesel engine, the fuel is ignited by
A. Spark
B. Injected fuel
C. Heat resulting from compressing air that is supplied for combustion
D. Ignition

Hint: The diesel motor is an inward burning motor where the start of the fuel which is infused into the ignition chamber is brought about by the raised temperature of the air in the chamber because of the mechanical pressure.

Complete answer:
In a diesel engine motor, the blend (fuel vapor + air), which is for the most part air, is compacted by cylinder, because of this high weight by cylinder, heat is delivered and temperature scopes to fuel's start temperature and burning beginnings. Henceforth in a diesel motor, the fuel is lighted by heat coming about because of packing the air that is provided for burning.
Diesel motors work by packing just the air. This expands the air temperature inside the chamber to such a serious extent that atomized diesel fuel that is infused into the burning chamber touches off unexpectedly. This stands out from sparkle start motors, for example, a petroleum motor (gasoline engine) or gas motor (utilizing a vaporous fuel rather than petroleum), which utilize a flash fitting to light an air-fuel blend. In diesel motors, sparkle plugs (combustion chamber pre-warmers) might be utilized to help to begin in chilly climate, or when the motor uses a lower pressure proportion or both.
The first diesel motor works on the "steady weight" pattern of continuous ignition and creates no discernible thump.

The correct answer is C.

Note:
Diesel engines are commonly used as mechanical engines, power generators and portable drives. They find widespread use in locomotives, construction equipment, automobiles, and countless industrial applications. There are two classes of diesel engines: two-stroke and four-stroke. Most diesel engines generally use the four-stroke cycle, with some larger engines operating on the two-stroke cycle.