CHARACTERISTICS OF DIESEL

What is diesel, types, properties, characteristics, specifications and terms

1. CHARACTERISTICS OF DIESEL P.ANJANEYULU JNTU ANANTAPURAM

2. CONTENTS What is Diesel Types of Diesel fuel Important factors or Properties Ignition quality of fuel expressed by different terms Characteristics of Diesel fuel Diesel fuel Specifications

3. DIESEL FUEL Diesel fuel in general is any liquid fuel  specifically designed for use in diesel engines, whose fuel ignition takes place, without any spark, as a result of compression of the inlet air mixture and then injection of fuel. Diesel fuel is a mixture of hydrocarbons obtained by distillation of crude oil. The important properties which are used to characterize diesel fuel include cetane number (or cetane index), fuel volatility, density, viscosity, cold behavior , and sulfur content.

4. Types of Diesel fuels Petroleum diesel Synthetic diesel Biodiesel Hydrogenated oils and fats DME(Dimethyl ether) Diesel fuel is produced from various sources, the most common being   petroleum . Other sources include biomass, animal fat,  biogas,   natural gas, and coal liquefaction.

5. Important factors which influence the choice of fuel: Viscosity of fuel Flash and fire point of fuel Water and sediment present Pour point of fuel Ash content of fuel Sulphur content of fuel Boiling range of fuel ie characteristics of fuel Specific gravity of fuel Carbon residue that will be formed Corrosive and acidity Ignition quality of fuel

6. Fuel viscosity Viscosity is simply a measure of resistance to flow. Viscosity decreases as the temperature increases. Low viscosity fuel produces a fine, atomized mist of fuel which improves its mix with incoming air to encourage a complete combustion for better power and lower emissions. High viscosity fuel tends to result in a heavier mist of fuel which can result in hard starting and white smoke issues. Flash point The flash point is a safety-related characteristic and defines the minimum temperature at ambient pressure at which a vapor-air mixture can be ignited in a closed space

7. Water and sediment content in fuel can also cause rusting and damage to fuel system components. Diesel fuel with a high water content can cause iron oxide particles to form inside the fuel tank. This causes internal rusting of fuel lines, pumps and injection components when the engine is not in use. Pour point of diesel fuel is important in engines which are operate to under extreme cold conditions. High pour point may interfere with starting a cold engine. Pour point is important in handling fuel between Storage and engine. Pour point of fuel should be 5.5 to 8.5°C units below the minimum anticipated temperature. Maximum pour point for diesel is -15.5ºC. Water and sediment present Pour point of fuel

8. Ash content of fuel Ash content in the fuel represents non combustible material, some of which is abrasive in nature. Ash content in diesel fuel builds up deposits. As such it should not exceed 0.12 percent by weight for the heaviest fuel and 0.01 percent for light fuel used in high speed engines . Sulphur content of fuel The sulfur content of diesel fuel has recently drawn a great deal of attention because of increased wear on the following components: Pistons Rings Valves Cylinders This increased wear is promoted by the corrosive effects of hydrogen sulfide in the fuel combined with sulfur dioxide (or sulfur trioxide), formed during the combustion process. The wear is less serious under constant loads and during high–temperature operation.

9. Boiling range of fuel Boiling range of fuel represents the temperature range corresponding to beginning and termination of vapourization of fuel and also the quantum of fuel that will vapourize at different temperatures. Volatility ie vapourization capacity of a fuel is measured by 90% distillation temperature. This is the temperature at which 90% of the fuel sample has distilled off. Lower this temperature higher is the volatility. Specific gravity of fuel The specific gravity of the fuel has no direct bearing upon the burning qualities of fuel. However, the above indicated limitations of viscosity more or less confine the limits of specific gravity to about 0.83 to 0.90 for airless injection engines, down to 0.94 for air injection engines

10. Carbon residue Carbon residue is the carbon left after evaporation and burning off of volatile matter from a sample of oil by heating. It indicates the tendency of the fuel to form carbon deposits on engine parts. A maximum carbon residue of 0.10 percent is allowable. C orrosiveness The fuel must not be corrosive, must not contain free acids. Otherwise it may damages the metal surfaces with which it comes in contact in storage and in the engine

11. Ignition quality of fuel/ Cetane rating Cetane rating is a measure of the ignition quality of a fuel. The ease at which diesel fuel ignites, and the manner in which it burns, influences engine starting and combustion roughness. Pure cetane is a colourless liquid hydrocarbon with excellent ignition qualities and is rated at 100. The higher the cetane rating, the shorter the lag time between the time the fuel enters the combustion chamber and the time it begins to burn.  A good quality diesel fuel with a high cetane rating has a lag time of approximately 0.001 seconds . Cetane rating requirements depend on the engine size, design, load and atmospheric conditions. For example, engines operating at higher altitudes or lower temperature demand a higher cetane fuel to start and operate correctly.  Typical cetane ratings for No. 2 diesel would be 46 – 48. No. 1 diesel is usually about 51 – 53 .

12. Ignition quality of fuel is expressed by different terms: Cetane number of fuel Self ignition temperature of fuel Critical compression ratio Diesel index Aniline point

13. Cetane number Cetane number ( cetane rating) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It plays a similar role for diesel as octane rating does for gasoline. The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel fuel's quality include (but are not limited to) energy content, density, lubricity, cold-flow properties and sulphur content . Self ignition temperature of fuel The   autoignition temperature  is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion .

14. Critical compression ratio Diesel engines normally have compression ratios between 14:1 to 25:1. Higher compression ratios mean a higher thermal efficiency, which means that theoretically maximum efficiency can be achieved at an infinite compression ratio Diesel index is an indication of the ignition quality of a diesel fuel. It can be determined by calculation from the specific gravity and the aniline point of the sample  Diesel index = (Aniline point * °API) / 100. Diesel index The  aniline point  is called the "aniline point temperature," which is the lowest temperature at which equal volumes of aniline (C 6 H 5 NH 2 ) and the oil form a single phase. The aniline point (AP) correlates roughly with the amount and type of aromatic hydrocarbons in an oil sample. The  aniline point (AP) correlates roughly with the amount and type of aromatic hydrocarbons in an oil sample. A low AP is indicative of higher aromatics, while a high AP is indicative of lower aromatics content. Aniline point

15. Must be clean, water, grit and all foreign matter must be removed by filtering or by a similar process Should be non corrosive, or at least without an corrosive agents as free acids Should have sufficient lubricating property so that there will not be undue wear of the fuel pump and the injector parts Must ignite easily for easy starting and smooth running of the engine Must burn progressively and smoothly which will avoid excessive cylinder pressures and a rough running engine Must burn completely and leave no carbon or other deposits and practically no ash in the engine cylinder. High viscosity fuels may cause smoky exhaust. Characteristics of Diesel fuel

16. Must have low carbon residue. High carbon residue may produce deposits of carbon and a gummy substance on pistons and cylinder liners. Deposits may cause sticking of piston rings and valve stems. Must have suitable volatility characteristics. Low volatility reduces maximum power output, increases fuel consumption and gives smoky exhaust. Such a fuel also makes starting of a cold engine more difficult. Characteristics of Diesel fuel

17. Characteristics Requirements A B C 1. Flash point( Pensky martens closed), min 55° 55° 55° 2. Kinematic viscosity centistokes at 37.8°C, max 2 to 7.5 2 to 7.5 15.7 max. 3. Carbon residue ( Ramsbottom -percent b weight) 0.2 0.2 1.5 4. Cetane number, min 45 40 -- 5. Diesel index 48 43 -- 6. Distillation , percent recovery at 360°C, min 90 90 -- 7. Copper strip corrosion for 3 hours at 100°C No.1 No.1 No.2 8. Water content percent by volume, max 0.05 0.05 0.25 9. Sediment percent by weight, max 0.05 0.05 0.10 10. Ash, percent by weight, max 0.01 0.01 0.02 11. Acidity (total) mg of KOH/g, max 0.5 0.5 -- 12. Sulphur, total percent b weight (max) 1.0 1.0 0.8 13. Pour point, max 6°C 6°C -- DIESEL FUELS BIS (ISI) SPECIFICATIONS 1460-1974

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