Two-Stroke Diesel Engine Reversing via Exhaust Valve Control
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Solution Overview
Problem
Large two-stroke diesel engines used in ships face challenges in quickly reversing direction, especially during emergency braking, due to their design which lacks a gearbox and clutch, resulting in prolonged braking times and excessive starting air consumption.
Innovation Solution
A method involving intelligent exhaust valve control, where the fuel supply is interrupted, and exhaust valves are strategically opened and closed to harness the ship's kinetic energy for reversing the engine direction without relying heavily on starting air, utilizing the propeller's energy to charge and discharge the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the fuel supply is interrupted to brake the ship, then the engine deceleration is achieved, but the braking time is excessively long and the ship stops only gradually due to mass inertia
Solution Approach 1:
The exhaust valves are opened in advance during a pre-braking phase before the main braking action, creating preliminary resistance to the pistons. This preliminary action reduces the engine speed to a limit value, preparing the system for the subsequent rapid reversal phase and reducing the overall braking time.
Solution Approach 2:
The braking process is divided into distinct phases: a pre-braking phase where exhaust valves are opened to create resistance, and a main braking phase where scavenging air supply is cut off. This segmentation allows each phase to perform its specific function optimally, achieving faster overall deceleration.
2Speed
If starting air is supplied to reverse the engine direction, then the propeller turns in the opposite direction, but the starting air consumption is excessive
Solution Approach 1:
The kinetic energy of the moving ship and the momentum of the propeller are converted into beneficial effects. By cutting off the scavenging air supply, the propeller's rotation drives the pistons in reverse, using the ship's own motion to assist the reversal process and reduce starting air consumption.
Solution Approach 2:
The system uses its own kinetic energy and momentum to facilitate the reversal. The propeller, driven by the ship's forward motion, automatically drives the pistons in reverse when scavenging air is cut off, making the system self-sufficient for the reversal action without requiring extensive external energy input.
3Device complexity
If the propeller is non-rotatably connected to the engine crankshaft, then the drive design is simpler, but the engine cannot be separated from the propeller during operation
Solution Approach 1:
The patent uses pneumatic control through exhaust valves and scavenging air supply to achieve operational flexibility. By controlling the air supply to cylinders, the engine can be braked and reversed without mechanical separation, using pneumatic means to decouple the engine's rotational direction from the propeller's inertia.
4Stability of the object's composition
If the engine continues to rotate in the original direction after fuel cutoff, then the propeller maintains momentum, but the reversal process is delayed
Solution Approach 1:
The exhaust valves are opened in advance during the pre-braking phase, creating preliminary resistance to the pistons while the engine is still rotating in the original direction. This preliminary anti-action begins to counter the engine's rotational momentum before the main braking phase, reducing the delay before reversal can occur.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables faster and more economical reversal of the engine direction with reduced starting air consumption, enhancing safety and operational efficiency, particularly in emergency situations.
Implementation Method 1
harness the ship's kinetic energy for reversing the engine direction without relying heavily on starting air, utilizing the propeller's energy to charge and discharge the engine
Implementation Method 2
the fuel supply is interrupted, and exhaust valves are strategically opened and closed
Data Source
AI summary
The invention relates to a reversing method for quickly reversing the rotation of an engine in the form of a longitudinally scavenged two-stroke large diesel engine, comprising a cylinder in which a piston is arranged to move back and forth between top dead center and bottom dead center, and an exhaust valve which is hydraulically actuated via an electronic control device by means of a hydraulic medium at a predetermined opening pressure via a valve hydraulic system. Preferably following a pre-braking phase, in a first braking phase, to reduce the rotational speed of the engine in a first direction of rotation, the fuel supply to the engine is interrupted and/or remains interrupted by means of a stop command to the control device.According to the invention, in the first deceleration phase below a predetermined limit speed, a plurality of the engine's exhaust valves are opened in a predetermined sequence, with the opened exhaust valves remaining open until the end of the first deceleration phase. In a second deceleration phase, at least all exhaust valves of those cylinders are closed simultaneously in which the supply of scavenging air through the cylinder's scavenging ports is prevented and in which the associated piston is in a compression stroke between a crank angle of 0° and 180°, so that in a kickstart phase following the second deceleration phase, the engine is rotated in a direction opposite to the first direction of rotation. The invention further relates to a computer program and an engine for carrying out the reversing method according to the invention.