One of the most influencing factors that prompts people to use diesel vehicles is its price. We are very much ignorant about the environment factors. There are various advantages of using a gasoline engine for commercial purpose. But there are instances where use diesel engine is must because of some of its very specific advantages.
- For heavy duty vehicles like trucks, buses it is very much common to use a diesel engine because of the requirement of very high torque and high power.
- In applications like generators, pumps etc are also run on diesel rather than petrol.
To meet the present emission norms in India which are already running late by 10 or 15 years or so then Europian countries, we need to design the diesel engines in such a way so that we can reduce its emissions upto an optimum level.
The main factors that are needed to be watched out are:
- Air flow optimisation
- Proper injection timing
- Exhaust aftertreatment
Air flow optimisation: It is very important to optimise the air flow into the cylinders to have the proper air fuel ratio which is around 14.7 for diesel engines. It varies at different speeds for different torque requirement. A non optimised air fuel mixture can lead to excess emission due to unburnt gases. The important factors are:
- Combustion chamber design
- Injector location
- Reduced crevice volumes
- Increased compression ratio
- Variable valve timing
- Electric assist
- Variable geometry
Proper Injection Timing: There are various ways of injecting the fuel into the cylinders like SPFI, continuous fuel injection. But the most advanced way to do it is MPFI which stands for Multi Point Fuel Injection. The advantages of using MPFI are listed below:
- More uniform A/F ratio
- Lesser number of strokes required
- Immediate response in sudden acceleration and deceleration
- ECM(Engine Control Unit) is used; more accurate A/F ratio
- Mileage is improved
The above factors are very much related to reduction in emissions.
Exhaust After-treatment: There are various ways of after treatment of exhaust gases which are very much costly but very effective in reducing emissions.
- Exhaust Gas Recirculation (EGR): here the exhaust that are coming out of the combustion chamber are recirculated to the intake through valves. These are ECU controlled and very effective in reducing CO and NOx emission.
- Diesel Particulate Filter: this technology is very much costly and used in very advanced vehicles. Use of this technology can reduce the emission of particulate to an effective level.
- Selective Catalytic Reduction: it also involves reduction in emission by treatment of exhaust gases with various catalysts.
- Three Way Catalytic Converter: with the help of catalyst like palladium and platinum these converters convert very harmful exhaust gases like CO, NOx and HC to less harmful CO2, O2, N2 and HO2.
A very popular technology that the OEMs are using nowadays is DOWNSIZING.
- Higher part load operation at open throttle
- Lower engine and vehicle weight
- Quicker engine warmup
- Lower friction due to lower no of cylinders
- Possibility of higher EGR rates at part loads
- Reduces cost
- Improved fuel economy
- Reduced CO2 emission
- Better packaging
- Better drivability
The above technologies are very much effective in reducing the emission level in diesel engines. But the main drawback is its cost. In the present scenario the use of dual fuel engines has also been popular in the urban areas. The diesel engines are being converted to bi fuel engines where the engines can be run with CNG being used as an alternative fuel. The CNG engines can give almost the same torque and power as the diesel engines with little compromisation in performance but with very less emissions.