Question 10 OSE02 - Assistant Engineer - OSV

The Correct Answer is B **Explanation for Option B (Correct Answer):** The illustration MO-0006, typical of generator set drive engines used in offshore supply vessels (often medium or high-speed diesel engines designed for robust power generation), usually depicts an engine utilizing a direct injection (DI) system. In a DI system, the fuel is injected directly into the main combustion space, which is characterized by an **open type combustion chamber**. This design maximizes thermal efficiency and is suitable for higher power output per cylinder, common in modern power generation applications. The corresponding cylinder head design often features a **flat fire-deck** (or cylinder head face) with the combustion bowl or cavity typically formed within the piston crown itself (sometimes referred to as the M-type or Omega bowl). Therefore, the combination of an open type combustion chamber and a flat fire-deck is characteristic of these generator set engines. **Explanation for Incorrect Options:** * **A) The engine uses turbulence chambers with a hemispherical fire-deck:** Turbulence chambers (or swirl chambers) are indirect injection (IDI) systems, which are less common and less efficient for large, high-output generator applications compared to DI systems. A hemispherical fire-deck suggests the cylinder head forms a dome-shaped combustion space, which is typical of spark-ignition gasoline engines or older IDI diesel designs, not the modern DI generator engines often found on OSVs. * **C) The engine uses pre-combustion chambers with a flat fire-deck:** Pre-combustion chambers are also a type of indirect injection (IDI) system. While effective for noise reduction and smooth running, they generally result in higher heat losses and lower overall efficiency compared to open (DI) chambers, making them less preferred for primary power generation sets where efficiency and specific fuel consumption are critical. * **D) The engine uses an open type combustion chamber with a hemispherical fire-deck:** While the engine uses an open type (DI) chamber, pairing this with a hemispherical fire-deck is structurally contradictory for a typical high-speed diesel engine. DI engines utilize a flat cylinder head face (fire-deck) to accommodate the centrally located injector and multiple valves, relying on the piston bowl for the necessary combustion volume shape.