Exhaust Analysis

Here Are The Exhaust Gas Questions And Answers Which Will Help You To Understand So Many Things -

 

Question: What Are Main Constituents Of Exhaust Gas, Its Effect And Technology Used To Reduce Them?
Answer: All Marine 2-stroke Diesel Engines Uses Low Quality Of Fuel To Reduce The Cost. This Low Quality Of Fuel Tends To Have Many Impurities. However Some Of Those Can Be Separated By Use Of Centrifuges But Some Residuals Are Unavoidable. In Order To Prevent Atmospheric Pollution And Its Impact On Human Health And Climate Change. There Are Several Limitations Have Been Imposed By National, Regional And International Authorities To Control The Air Pollution.

Constituents Of Exhaust Gas:
NOx- Formation Of Nitrogen Oxides Is Due To Combination Of Nitrogen And Oxygen From Air At Higher Combustion Temperature. These Oxides Are Regarded As Carcinogenic Compounds And Contribute To Photo-chemical Smog Formation And Acid Rains.
Impacts:
1. Cause Acid Rain Thus Acidification Of Soil.
2. Affects Air Quality.
3. Elevates The Level Of Ozone And Produces Hazardous Organic Compounds.
4. Cause Green House Effect At Low Temperature.

Technology To Reduce NOx
1. Modification Of Combustion Process:
I) Increasing Injection Pressure, Delaying Injection Timing
Ii) Increasing Compression Ratio
Iii) Alteration Of Air - Fuel Ratio
Iv) Optimization Of Induction Swirl
V) Increasing No. Of Injectors And Modification In Its Design

2. Modification In Air Intake System
I) Scavenge/charge Air Cooling
Ii) Increasing Scavenge/charge Air Pressure

3. Direct Water Injection: It Reduces NO Discharge By 50 To 60 %

4. Exhaust Gas Recirculation: It Reduces Oxygen By 15 % Thus Reduction In NOx Formation

5. Humid Air Motor (HAM): Dilution Of Charge Air By Water Reduces NOx By 70 %. But This Is Not A Very Effective Method For NOx Reduction. Use Of HAM Increases SFOC And Produces Smoke. There Is Also High Investment Cost And One Important Disadvantage Is It Reduces The Net Energy Available At T/C.

6. SCR: Selective Catalytic Reduction Is Widely Used For The NOx Reduction And Reduces 85-95 % And Doesn't Affect Engine Performance. In SCR Method Exhaust Gas Is Mixedwith NH3 And Passed Through A Layers Of Catalyst At 300 - 400 Degree C To Reduce NOx Into N2 And H2O.

SOx - Oxides Of Sulphur Produced During Due To Combustion Of Sulphur In The Fuel. Amount Of SOx Formation Depends Upon The Concentration Of Sulphur In The Fuel Oil. The Prime Constituent Of SOx Is SO2. It Has Very Adverse Effect On Health And Atmosphere. Impacts: 1. It Has Unpleasant Order And Irritates Mucus Membrane. 2. It Is A Major Source Of Acid Rain. 3. Sufficient Concentration Of SO2 Can Adversely Affect The Lungs Function. Technology To Reduce SOx 1. Use Of Scrubbers Can Remove Majority Of SOx Emission From The Exhaust. 2. Use Of Low Sulphur Fuel (most Efficient Method To Reduce SOx Emission). 3. Speed Reduction: Reduction In Speed By 10 % Gives 20 % Reduction In Fuel Consumption Over Same Distance.

HC (Hydrocarbons) - It Is Produced Due To Incomplete Combustion Of Fuel. It Has Unpleasant Order And Carcinogenic Compound. However Amount Of HC Is Very Low If Combustion Is Proper.

CO - It Is Formed Due To Incomplete Combustion I.e. Due To Local Shortage Of Air During Combustion. It Is Highly Toxic Compound And It Is Very Hazardous At Higher Concentration.