Question 25 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is A. **Explanation for Option A (1 being correct):** Figure 1 represents a **multi-hole nozzle** (typically featuring 4 to 12 holes). This type of nozzle is the standard choice for **open type combustion chambers featuring direct injection** in medium and high-speed diesel engines, such as those typically found in harbor tugs. The design allows the fuel spray to be precisely distributed across the large volume of the open combustion chamber, ensuring efficient mixing of fuel and air (turbulence) to achieve complete combustion and high power output. **Explanation for why other options are incorrect:** * **Option B (2):** Figure 2 represents a **pintle nozzle**. Pintle nozzles are generally used in smaller, high-speed engines utilizing **pre-combustion chambers** or **swirl chambers** (indirect injection systems). They are not typically used for direct injection into large, open combustion chambers of medium-speed marine engines due to their limited spray coverage. * **Option C (3):** Figure 3 represents a **long stem pintle nozzle** or an early variation of a single-hole nozzle designed for specific chamber types, sometimes used in pre-chamber designs. Like the standard pintle nozzle, it lacks the multi-spray pattern necessary for the efficient filling and combustion in a large, open, direct-injection chamber. * **Option D (4):** Figure 4 represents a **single-hole nozzle** (or possibly a throttling pintle nozzle variant). Single-hole nozzles create a highly concentrated, narrow spray pattern, which is unsuitable for achieving uniform mixing across the wide volume of an open combustion chamber. This leads to poor combustion efficiency and localized high temperatures.