Question 1 OSE02 - Assistant Engineer - OSV

The Correct Answer is A **Explanation for Option A (Correct):** Option A is correct because it accurately describes the fundamental operating principle of a compression-ignition (CI) engine, commonly known as a diesel engine. In a diesel engine cycle, the intake (or charge) air is drawn into the cylinder and then highly compressed by the piston. This rapid compression significantly raises the temperature of the air (adiabatic heating) well above the auto-ignition temperature of diesel fuel. Near the end of the compression stroke, diesel fuel is injected into this superheated air, causing immediate and spontaneous ignition without the need for an external ignition source like a spark plug. **Explanation for Incorrect Options:** **B) Ignition is achieved by a high voltage electric spark induced across the gap of a specially designed spark plug.** This option describes the ignition method used in a spark-ignition (SI) engine, such as a gasoline or natural gas engine. Diesel engines do not use spark plugs for normal running ignition. **C) Ignition is achieved by the heat of compression created by compressing the air/fuel mixture within the cylinder into a relatively small volume.** This option is incorrect because it describes compressing an *air/fuel mixture*. If a pre-mixed charge of air and diesel fuel were compressed to the high ratios typical of a diesel engine, auto-ignition would occur prematurely and uncontrollably (a phenomenon known as knocking or detonation). In a true diesel cycle, only pure air (or charge air) is compressed, and the fuel is injected only *after* compression is complete. **D) Ignition is achieved by intense heat by passing electric current through the element of a specially designed glow plug.** This option is incorrect. While glow plugs (or sometimes block heaters) are used in some smaller or auxiliary diesel engines, particularly in cold weather, their function is solely to pre-heat the combustion chamber or the intake air *before* starting the engine (to assist initial compression-ignition). Once the engine is running and up to operating speed, the heat of compression alone is sufficient to cause ignition; the glow plugs are not used to achieve continuous ignition while running.