Diesel engine have following advantages over petrol engine.
1- Diesel engine burns fuel at high compression ratio instead of using spark plug and they are also un-throttled which is why diesel engines are more efficient compared to petrol engine.
2- Thermal efficiency of diesel engine is higher than that of petrol engine which means that they can convert more of the heat supplied into useful mechanical work and waste less of it into the environment.
3- Diesel engine are low carbon and other greenhouse gas emitters. Greenhouse gases are responsible for elevating the earth’s temperature.
4- Diesel engines work at lower RPMs contrasted with a petrol engine which causes less frictional losses. The pieces of the diesel engine are thicker because of the high pressing factor they need to withstand. This makes them more strong along these lines less inclined to fall flat. Diesel being a light oil likewise greases up the burning chamber each time it's being utilized. This additionally makes it last more as less grinding approaches less wear which thus implies less maintenance required.
5- These engines are worked for more force while being more effective than a petrol engine. The explanation is the pressure proportion. As diesel engines are self-touching off, they need to produce sufficient pressing factor in the burning chamber which would make the diesel light. This increment in pressure proportion implies more force/torque delivered when ignition happens. The diesel engine likewise has quicker ignition which implies more force/torque too.
6- As they produce more force/torque, diesel vehicles are more qualified for pulling substantial things. Force decides the rotational power of the vehicle and the more force/torque a vehicle has the more burden it can convey without losing execution. This makes the diesel-controlled vehicle ideal for weighty takes.
7- From less visits to the service station to more grounded engine parts that don't flop as regularly, diesel engines are more solid than petrol over the long haul. They are costlier to fix than petrol however they flop less regularly when contrasted with petrol along these lines making the chances for diesel.
Emissions from Diesel Engine and Effect on Environment and Human Health:
Transport have played an important role in escalating climate change and increasing environmental pollution. According to a report of International Energy Agency in 2012, transport contributes to 22% of carbon emissions which is second largest in the world. Transport is the main source of urban pollution especially in the developing world due to the very limited use of carbon control technology.
Diesel is chemically made up of carbon and hydrogen in different proportion. In a diesel engine, fuel is sprayed onto a highly compressed air inside the cylinder which ignites the combustion. High pressure inside the cylinder triggers auto combustion of diesel. If we see from ideal thermodynamic equilibrium perspective, the combustion process should produce CO2 and H2O. But, due to many reasons such as combustion temperature and timing, air–fuel ratio and turbulence etc., different harmful products are produced during combustion. Carbon monoxide (CO) is emitted due to the incomplete combustion when the oxidation process does not occur completely. It is largely dependent on air fuel mixture. When the air fuel mixture is rich and air is deficient, all the carbon can’t burn which causes CO emission. It is a colorless and odorless gas. When we inhale air, it is transported to lungs and subsequently transmitted to blood stream. It binds with hemoglobin and hinders its capacity to transfer oxygen. Depending upon the concentration of CO inhaled, it can damage different organs and can also cause confusion and slow reflexes.
Brief Introduction of Emission Reduction Techniques for Diesel Engines:
Due to adverse effect on both humans and environment, scientists have adopted different methods to reduce emissions. Most of the researchers has worked on to reduced NOx emissions and it has the highest percentage among other pollutants. Lean NOx trap (LNT), Exhaust gas recirculation (EGR), and Selective Catalytic Reduction (SCR) are the most focused technologies by researchers. In EGR, exhaust gas is recirculated in the combustion chamber with fresh air. LNT technology works by storing NOx under lean mixture conditions and use it when the mixture is rich. SCR is an advance technology that uses a liquid agent in the exhaust stream of diesel engine. Separate systems for emission control i.e. Diesel oxidation catalyst (DOC), Diesel particulate filter (DPF), and Selective catalytic reduction (SCR), are also extensively used.