Question 1 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is B **Explanation for Option B (Correct):** Diesel engines, also known as Compression-Ignition (CI) engines, operate by drawing in only air (intake/charge air) during the intake stroke. This air is then highly compressed during the compression stroke. The act of rapidly compressing the air into a small volume raises its temperature significantly (the heat of compression). When the air reaches temperatures far exceeding the auto-ignition point of diesel fuel (typically around 700 to 1000 °C), the fuel is injected directly into this superheated air, causing immediate and spontaneous combustion (ignition). **Explanation for Other Options (Incorrect):** * **A) Ignition is achieved by the heat of compression created by compressing the air/fuel mixture within the cylinder into a relatively small volume.** This is incorrect because diesel engines compress only air, not an air/fuel mixture. Compressing a pre-mixed air/fuel charge is characteristic of gasoline (Spark-Ignition) engines, which would lead to uncontrolled pre-ignition (knocking) if compressed too highly. * **C) Ignition is achieved by a high voltage electric spark induced across the gap of a specially designed spark plug.** This describes the ignition method used in gasoline/petrol engines (Spark-Ignition engines), not standard operational diesel engines. * **D) Ignition is achieved by intense heat by passing electric current through the element of a specially designed glow plug.** While glow plugs (or sometimes block heaters) use electric current to generate heat, they are used only for assisting cold starting in smaller or medium-sized diesel engines by preheating the combustion chamber. Once the engine is running and up to operating temperature, the glow plugs are switched off, and ignition relies solely on the heat generated by compression.