Question 2 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is D **Explanation for D (Uniflow):** The illustration MO-0122 (which depicts a typical large, slow-speed, two-stroke marine diesel engine, often manufactured by companies like MAN B\&W or Sulzer) shows an engine design characterized by: 1. **Scavenging Ports** located near the bottom of the cylinder liner (controlled by the piston). 2. **Exhaust Valve** located at the top of the cylinder head. In this configuration, the fresh scavenging air enters the cylinder through the ports at the bottom and flows upwards, pushing the burnt exhaust gases out through the open exhaust valve at the top. This straight-line, one-directional flow from bottom to top is known as **Uniflow scavenging**. This method is mechanically complex (due to the requirement for the exhaust valve mechanism) but provides the highest scavenging efficiency because it minimizes mixing between the fresh air and the residual exhaust gases. It is the standard design for modern large two-stroke marine propulsion engines. **Explanation for Incorrect Options:** * **A) Cross-flow:** This pattern involves both the scavenging ports and the exhaust ports being located opposite each other on the cylinder liner walls. The air flows directly across the cylinder from the inlet side to the exhaust side. This method is rarely used in large modern marine engines due to very low scavenging efficiency and is typically only found in very small, older engines. * **B) Return-flow:** This term is not a standard, recognized designation for a primary scavenging flow pattern in internal combustion engines. It may sometimes be used synonymously with 'Loop' scavenging, or simply 'Loop/Reverse flow' in non-technical literature, but it is not the accurate technical term. * **C) Loop:** Loop scavenging (also known as Reverse-flow or Tangential scavenging) involves both the scavenging ports and the exhaust ports being located in the cylinder liner, but side-by-side or slightly offset. The air flows into the cylinder, loops up, and then flows back down toward the exhaust ports. While highly efficient in some medium-sized high-speed engines (like some older Sulzer two-strokes), it is less efficient than Uniflow and does not match the design shown (which clearly includes an exhaust valve in the cylinder head).