Skip to main content

Formation of NOx


Nitrogen oxides are the major air pollutants and pose a challenge to engine manufacturers to meet the limits set forth by the MARPOL Annex VI. 

Combustion of fuels is the primary anthropogenic source of formation of nitrogen oxides, While Nitric oxide (NO) and nitrogendi-oxide are usually grouped together as NOx emissions, nitric oxide is the predominant oxide of nitrogen produced by combustion process. Therefore, it is an important minor species in the combustion because of its contribution to air pollution. 

The principal source of NO is the oxidation of atmospheric (molecular) nitrogen. However, if the fuel contains significant nitrogen, the oxidation of the fuel nitrogen-containing compounds is an additional source. In the combustion of fuel that contains no nitrogen , nitric oxide is formed by three chemical mechanisms that involve nitrogen from the air. 

The three principal mechanisms are:
i) The thermal or Zeldovich mechanism
ii) The Fennimore or prompt mechanism
iii) N2O – the intermediate mechanism

The formation of NOx is a function of combustion temperature (i.e. high peak pressure, high compression ratio, high rate of fuel delivery, etc) and residence time. Therefore, the fundamental principle is regardless of what measures you take to bring down the NOx emission levels, they must be effective in keeping the peak temperature down, low and residence
time to minimum.


What Causes NOx in Marine Engines?
  1. High Cylinder Temperature and Pressure during combustion process
  2. Heavy Load on the engine or engine unit.
  3. Improper air and fuel ratio for combustion.
  4. High Temperature of intake or scavenge air inside the cylinder.
  5. Over heated cylinder jacket due to poor heat transfer by jacket cooler.
  6. Jacket water temperature is on the higher side.
  7. Bad quality of fuel used for engine.

Labels:

Comments

Post a Comment

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
9 comments
Read more

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
14 comments
Read more

Gravity Disc

Oils containing water can only be de-watered in a perfect manner if the bowl is accurately adjusted to the difference in densities of oil and water. The gravity disc with proper inner diameter i.e. with the diameter that corresponds to the difference in densities of the oil-water mixture to be treated should, therefore, be inserted in the bowl, This disc can be chosen from the set of disc provided with the separator. The inner diameter of the disc to be chosen can be determined by:  Calculation   Experiment The general rule is : Small diameter gravity disc when treating heavy oil Large diameter regulating ring when treating light oil Determining the size of gravity disc by calculation: For a given separating temperature, the inner diameter of the gravity disc and if the desired density of the oil can be determined from the diagram, provided that the density of the oil at a temperature ranging 15℃ and 90℃ is known. For example; Given: Density of oil at 20℃            ρ oil
7 comments
Read more