Dual Fuel And Multi-fuel Engines ai71

DUAL AND MULTIFUEL ENGINE

Introduction • Shortage of liquid fuel and gaseous fuels being cheaper than liquid fuels gave birth to dual fuel engines. • From recent air and water pollution concern it became necessary to utilize sewage gas. • Gaseous fuels have high self-ignition temperature and burn efficiently.

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‰ Duel-fuel

operation combines the possibility of operating a diesel engine on liquid fuels such as diesel oil or gas oil and on gaseous fuels such as natural gas, sewage gas and cook oven gas.

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Working Principle

• Works on diesel cycle. • Gaseous fuel (primary fuel) is added to air inducted into the engine or supplied by supercharger. • The mixture of air and gaseous fuel gets compressed in the cylinder. • Liquid fuel called pilot fuel injected near the TDC acts as a source of ignition. • Gas-air mixture ignites establishing a number of flamefronts. • In a dual-fuel engine combustion starts similar to CI engine, but it is propagated by flame-fronts as in SI engine. 4

Working Principle

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Gas mode • High efficiency and low emissions • Automatic and instant transfer to diesel operation in alarm to situations • Transfer diesel at any load operation

Diesel mode • As an ordinary diesel engine • Transfer to gas operation preferably at load part • Pilot fuel injection in operation

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Performance of Dual-Fuel engines

• Produce equal power when operating on liquid fuels as with gaseous fuel. • Dual fuel engines are slightly more efficient to conventional diesel at full • However, the maximum output is load. the same. about • Efficiency of dual in part load is poor. slightly • Typical diesel efficiency is 41%, and dual efficiency is 38.5. 7

Advantages of Dual Fuel Engines • Efficient utilization of cheap gas from various available sources. • Gas burns without leaving any residue pollution). (no

• Clean combustion results in reduced wear of engine parts and reduced consumption of lubricating oil. 8

Advantages of Dual Fuel Engines

• Increased utility of the power plant as the versatility of change-over from gas to diesel andamount vice-versa. • Only a small of liquid fuel needed to run engine. • Suitable for total energy installation (sewage gas) 9

Advantages of Dual Fuel Engines • Can be used to produce synthetic gas, which is a mixture of CO and H2. • Ideal for LPG tankers as they can utilize the gas which evaporates.

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Factors affecting combustion in a dual fuel engine • Pilot fuel quantity

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• Injection timing

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• Effect of Cetane number • Effect of inlet temperature

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• Effect of type of gaseous fuels

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• Effect of throttling • Effect of mixture strength

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Main type of gaseous fuel & their requirement

• Natural gas • Sewage gas • LPG • Town gas • Hydrogen gas • Clean • Dry • Minimum calorific value gas 4500 kcl/cm3 light fuel oil 10,200 kcl/kg 18

Knock control in dual engine • Excess supply of air • Use of cold combustion air • Increased cooling of piston • Use of additives • Reducing the pressure of gaseous fuel the

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Multi-fuel Engines

• A multi-fuel engine is one which would operate satisfactorily with substantially unchanged performance and efficiency, on a wide verity of fuels ranging from diesel oil, crude oil to lighter fuels like gasoline and even normal lubrication oil. • Mainly developed for military requirements. • Has good idling and part load efficiency and low exhaust smoke. 20

• Should have high compression ratios as gasoline have low cetane numbers. • Must be capable of starting at subzero temperatures. • Large stroke/bore ratio gives a compact combustion chamber so that it remains hot in all conditions of speed. • An open combustion chamber is suited as in a pre-combustion chamber, additional heat losses due to throat occur (e.g., spherical or M-combustion chamber). 21

Difficulties • Tendency of vapor lock while using lighter fuels. • Tendency of increased wear due to lower lubricity of gasoline. • Requirements for injecting different volumes of fuel depending on their heating values and compressibility.

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References

1. Crouse WH, and Anglin DL, (1985), Automotive Engines, Tata McGra

Hill. 2. Fergusan CR, and Kirkpatrick AT, (2001), Internal Combustion John Wiley & Engines, Sons. 3. Gill PW, Smith JH, and Ziurys EJ, (1959), Fundamentals of I. C. Oxford and IBH Pub Engines, Ltd. H, (1999), Vehicle and Engine Technology, Arnold Publishers 4. Heisler 5. Heywood JB, (1989), Internal Combustion Engine Fundamentals, McGraw Hill.JB, and Sher E, (1999), The Two-Stroke Cycle Engine, Tayl 6. Heywood & Francis. 7. Mathur ML, and Sharma RP, (1994), A Course in Internal Combustio Engines, Dhanpat Rai & Sons, New Delhi. 8. Pulkrabek WW, (1997), Engineering Fundamentals of the I. C. Engin Hall. Prentice 9. Rogers GFC, and Mayhew YR, (1992), Engineering Thermodynamic Wisley. Addison 10. Stone R, (1992), Internal Combustion Engines, The Macmillan Pres London. Limited, 11. Taylor CF, (1985), The Internal-Combustion Engine in Theory and & 2, The Practice, Vol.MIT 1 Press, Cambridge, Massachusetts. 23

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