18 February 2016

Dual Fuel and Multi-Fuel engine

Dual Fuel Engines :

The two fuel can be taken in varying proportion use in the engine this engine usually called dual fuel engine. The engine ran on gaseous fuel ignited by oil injection into the cylinder.

Last few decades more focus on dual fuel engine due to the shortage of liquid fuels.

Dual fuel engines run on both gas and diesel when operating in gas mode NOx emissions are roughly 80 per cent lower CO2 emissions are considerably reduced because of the lower carbon content of the fuel while emissions of sulphur oxides are virtually non-existent.

Working Principle :

The dual fuel engine works on diesel cycle. In this engine gaseous fuel is used as primary fuel is inducted into the engine or supplied by super chargers. and liquid fuel is called pilot fuel or secondary fuel.

In a four stroke engine gas is supplied in the inlet manifold where it mixed with air and makes a homogeneous mixture. In a two stroke engine gas may be injected at low pressure and directly into the combustion chamber. This mixture of air and fuel is compressed in the cylinder.

Liquid fuel acts as a source of ignition in this engine and it injected near TDC. then gas-air mixture ignites and establishing a number of flame-fronts. Thus combustion starts smoothly. 

In a dual fuel engine combustion starts similar to CI engine but its propagated by flame-front as in SI engine. Thus power output of this engine is normally controlled by changing the primary fuel.

Gas Mode :
  • High efficiency and low emissions
  • transfer to diesel operation at any load.
Diesel Mode :
  • Ordinary Diesel Engine
  • Transfer to gas operation preferably at part load
  • Pilot fuel in injection system

Performance of Dual Engine :

Dual fuel engine is more efficient to conventional diesel engine at full load.

Maximum output is same as conventional diesel engine.

Efficiency of dual fuel engine in a part load condition is poor.

Diesel efficiency 41 % and duel efficiency 38.5 %.

Advantages of Dual Fuel Engine :

Gas burns neatly and exhaust is clean so not leaving any residue gases it helps to reducing air pollution.

Reduced wear of the engine parts.

Reduced consumption of lubricating oil.

Efficient utilization of cheap gas available from various source.

Small amount of liquid fuel is needed to run engine.

Highly suitable for total energy installation.

Can be used to produced synthetic gas.

For LPG tankers utilized mainly evaporates during transportation.

Types of gaseous fuel used in Dual fuel engine :

  • Natural Gas
  • Sewage Gas
  • LPG
  • Town Gas
  • Hydrogen Gas

Multi-Fuel Engines :

Multi-fuel engine is one which can be operate with wide variety of fuels ranging from diesel oil, crude oil, gasoline and lubricating oil and it gives comparable performance and efficiency. The main reason for developing multi-fuel engine is for military requirements.

Multi-fuel engine have good efficiency at part load conditions.

In Multi-fuel engine should have high compression ratio as gasoline have low cetane numbers.

Difficulties :

Tendency of vapour lock while using lighter fuels.

Tendency of increased wear due to low lubrication.

Requirements for injecting different volumes of fuel.

Characteristics of Multi-fuel Engine :

Must have good combustion efficiency.

Combustion chamber temperature must be comparatively higher.

Easy starting under sub-zero temperature conditions.

Must have low exhaust smoke and noise levels.

Higher compression ratio

Stroke to bore ratio as high as 1.35:1 has been used.