Automobiles with compression ignition engines emit nitric oxides and soot. A significant portion of energy is lost in the formation of the harmful gases. The exhaust emissions are attributed to poor air-fuel mixing. Attempts to reduce the nitric oxide emissions using strategies such as multiple injections, late fuel injection timing and exhaust gas re-circulation tend to increase soot emission which is undesirable. Devices, such as diesel particulate filters and selective catalytic reactors, are also not acceptable as these increase fuel consumption and thus add to the costs of the travel.
So, how can we minimize the formation of these toxic gases and particle emissions without increasing fuel consumption?
Devendra Deshmukh and Vasudev D Chaudhari from IIT Indore thought of reducing the temperature at which combustion takes place. This could reduce the formation of nitric oxides. To bring down the combustion temperature, they tried mixing diesel with petrol.
They used commercially available diesel as base fuel. And they selected a diesel-petrol blend with twenty-five per cent petrol by volume, as second fuel. ‘The use of a higher percentage of gasoline was avoided to reduce the self-lubrication of the fuel pump”, explains Vasudev Chaudhari.
For their experiments, they used a single cylinder, naturally aspirated, water cooled light duty diesel engine. They equipped the engine with a fuel injection controller system, a solenoid injector and a hot exhaust gas re-circulation loop.
The team conducted the experiments at medium load condition and constant engine speed. They investigated the combustion, engine performance and clean emission characteristics of diesel and diesel-gasoline blends.
For early fuel injection, the team found that the change in fuel reactivity and charge dilution improve the air-fuel mixing. It extends the start of combustion and combustion burn duration.
The team found that, with undiluted charge, the rate of heat release is high. So is the rate of increase in pressure. But when diesel is diluted with petrol, the heat release rate and the rate of increase in pressure were lower. The team observed near-zero nitrogen oxide-soot emissions with very low hydrocarbon and carbon monoxide emissions.
Fuel consumption decreased with the premixed combustion. The team claims that the load-carrying capacity of the engine also increases with the diesel-petrol blend.
Automobiles running on liquid fossil fuels are the major sources of air pollution. ‘Our findings hold promise of protecting the environment along with improved efficiency of engines’, says Devendra Deshmukh, IIT Indore.
Fuel, 266: 116982 (2020); DOI: 10.1016/j.fuel.2019.116982
Freelance Science Writer, Cuttack
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