Skip to main content

Advantages of Super Long Stroke Engines


Super long stroke means increased swept volume allowing more mass of air to be drawn into the cylinder which in turn allows more fuel to be burnt, hence increasing power output. Super long stroke increases piston travel time and thereby decreases crank speed so more time for combustion during the stroke. The efficiency of Large dia propellers is best at slower RPM.With super long stroke we can have slower RPM of engine with no change in mean piston
speed of the engine.


Classification of engine based on stroke/bore ratio:

Short stroke : 2.6-3.2
Long stroke : 3.2-4.0
Super-Long stroke : 4.0-4.7
Ultra-Long stroke : >4.7

These engines allow for low quality of fuel to be burnt as there is more time available for fuel combustion. With increase in stroke length we have an advantage of burning dirty fuel/low grade fuel at min rev/low speed with good efficiency. This also results in proper utilization of fuel resulting in reduction of NOx generation.
An engine cylinder with longer stroke-to-bore ratio will have a smaller surface area exposed to the combustion chamber gases compared to a cylinder with shorter stroke-to-bore ratio. The smaller area leads directly to reduced in-cylinder heat transfer, increased energy transfer to the crankshaft and, therefore, higher efficiency.

Scavenge air of the cylinder is also affected by the stroke-to-bore ratio in a uniflow-scavenging, two-stroke engine. As the stroke-to-bore ratio increases, the distance the fresh air has to travel between the intake ports at one end of the cylinder and the exhaust ports at the other end correspondingly increases. This increased distance results in higher scavenging efficiency and, as a result, lower pumping work because less fresh air is lost via charge short circuiting. Again, it improves fuel combustion by ensuring more fresh air.

These engines have a better power to weight ratio and since more heat is converted into useful work, an increased thermal efficiency.

Comments

Popular posts from this blog

Load Line & Why it is Important

Merchant ships have a marking on their hull know as the Plimsoll line or the Plimsoll mark, which indicates the limit until which ships can be loaded with enough cargo, internationally, the Plimsoll line on a ship is officially referred to as the international load line. Every type of ship has a different level of floating and the Plimsoll line on a ship generally varies from one vessel to another.  All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line. There are two types of Load line markings:- Standard Load Line marking – This is applicable to all types of vessels. Timber Load Line Markings – This is applicable to vessels carrying timber cargo. These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background/black on a light background.  The comp

Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division  IMO Symbol B Class Division  SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships. The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. Types of Divisions: "A" Class "B" Class "C" Class "A" Class: "A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria: They are constructed of steel or equivalent material They are suitably stiffened They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. they are insulated with approved non-combustible materials such that the average tempera

Pump Shaft Alignment Procedure

Types of shaft alignment methods: Visual Line-Up Straightedge/Feeler Gauge Rim and Face Cross Dial Reverse Dial Laser Visual Line-Up The visual line-up method is the most common method of alignment. Used in initial installations, visual line-up allows technicians to analyze the working conditions and feasibility of installation. Straightedge/Feeler Gauge Straightedges are used to determine the offset between coupling halves. Corrections are made under all four of the machines feet. Feeler gauges or taper gauges measure the gap between coupling halves at the bottom and top of the coupling. Rim and Face This method is similar in principle to using a straightedge and feeler gauge, but more accurate since dial indicators are used. The rim reading measures the offset between the coupling halves. The face reading measures the angular difference between the faces of the coupling. Changes are calculated with the same formula as the straightedge/feeler gauge met