Diesel Engine- Open-w vs Omega Piston
IC Engine
IC Engines can be broadly classified as two types :-
- Gasoline Engine
- Diesel Engine
Introduction
In this project, we will see the effect of piston profile change in acheving cleaner combustion. It is also called Compression Ignition Engine.
Fig.1.1:-Scehamatic Diagram of Diesel Enigne
Here the air is compressed and the fuel is sprayed using the fuel injector. The Engine has both inlet and exhaust valves, apart from the fuel injector. It has a four-stroke combustion cycle.
A few important parts in an Diesel Engine:-
Combustion Chamber :-Internal combustion engines can contain any number of combustion chambers (cylinders), with numbers between one and twelve being common, though as many as 36 have been used. Having more cylinders in an engine yields two potential benefits: first, the engine can have a larger displacement with smaller individual reciprocating masses, that is, the mass of each piston can be less thus making a smoother-running engine since the engine tends to vibrate as a result of the pistons moving up and down. Doubling the number of the same size cylinders will double the torque and power.
Valves:- All engine systems will have valves for the precise admitance of air and fuel in the combustion chamber. Here, the inlet valves alow the admitance of air and the exhaust valve alow the escaping of exhaust gases.
Piston:-In the Compression Ignition Engine the pistoncompresses the un-burnt air. After which the fuel is sprayed using the fuel injector leading to combustion and release of energy. The piston is a moving component contained by a cylinder and gas tight piston rods. The piston is to transfer force from expanding gas in the cylinder to the crankshaft through the connecting rod.
Connecting Rod:-A connecting rod is a rigid member which connects a piston to a the crankshaft in the diesel engine. Together with the crankshaft, it forms a simple mechanism that converts reciprocating motion into rotating motion.
A detailed animation on how the Diesel Engine works:-
https://www.youtube.com/watch?v=fTAUq6G9apg&feature=youtu.be
CI Engine has the following strokes :-
- Suction Stroke:- Air is inducted into the CI Engine when the inlet valve is open & the ehaust valve close. Suction of air into the Automotive Engine system requires an inductor with an air filter. These system prevents dust particles even of the order 1 micron entering the engine system.
- Compression Stroke:- Here, the air is compressed till the clearence volume and both the valves remain closed during the stroke. The air pressure increase during this stroke.
- Expansion stroke:-As shown in the video the diesel injection starts only at the end of the compression stroke. A constat pressure is maintained throughout this process and the high pressure maintained leads to the combustion of diesel, ultimately proving energy to the locomotive. Due to combustion process there are varied harmful exhaust gases emitted such as Nox, SOx, HC, CO &CO2
- Exhaust Stroke:-In this stroke, the exhaust gases escape from the engine chamber through the exhaust valves. Here the exhaust valves are open , while the inlet valves are closed. The exhaust gases escaping travel via the exhaust system before being released into the atmosphere.
Fig1.2:-Schematic diagram of four cycles involved in the Diesel engine
As seen in the PV-diagram both the suction stroke and the exhaust stroke are adiabatic process . Combustion and power delivaery are both constant pressure and volume respectively.
2.Emission System
Post the exhaust stroke the burnt gas has to be released into the atmosphere. For this we employ a separate exhaust system.Due to incomplete combustion HC & CO gets emitted. A black powder or flaky substance consisting largely of amorphous carbon, produced by incomplete combustion of fuel is called Soot(HC Emission) .
Due to the high temperature involved in the combustion process in the case of diesel engine Nitric oxides are formed. Sulphur dioxide is produced due to the sulphur preasent in the diesel, which is oxidised during combustion process.
When the exhaust valves are open the burnt gases enter the exhaust pipe which is connected to the engine via the flange.
Figure 2.1:-A scematic view of the exhaust system
In the entire exhaust network there are three important parts CAT, muffler & resonator. They act as a resistance and don\'t alow the engine to breathe. This will ensure the piston puts in more effort to make the exhaust gas to reach the tail pipe.
Figure 2.2:-CAT in the exhaust system.
Figure 2.3:-Resonator in the exhaust system.
Figure 2.4:-Muffler in the exhaust system
A clear idea about the working of the Exhaust system and Catalytic system can be viewed in the video:-
https://www.youtube.com/watch?v=1zH22Qpe2GA&feature=youtu.be
3.Cleaner Combustion
We employ two piston designs namely open-w piston & bowl piston and employ which one provides cleaner combustion. In reality, as seen above the Diesel is combusted with atmospheric air air.
Diesel is an hydro-carbon and atmospheric air(which is input) has both oxygen & nitrogen.
When there is 100% clean combustion reaction in diesel engine the reaction is as follows:-
Eq.3.1:-Clean combustion of diesel
However, 100 percent clean combustion is never achieved hence there is emission of toxic gases like CO, Hydrocarbons apart from carbondioxide.
Due to high temperature involved in the the combustion process there is a formation of oxides of Nitrogen which are fatel, if present in high concentration in our environment.
For both the piston geometries a sector model is made to analyze the emissions. Here the sector angle is set at 60 Degrees from the boundary file.
We compare both the piston designs with IMEP & Power values.
4.Piston Profile & Simulation Results
The sector angle is set at 60 Degree to obtain the sector geometry for both Omega & Open-w piston.
Figure 4.1:-A sector view of the Omega piston
Cut Plane videos for Omega Piston:-
Presence of Hydro Carbon:-
Presence of Carbon Monooxide (CO):-
Presence of Soot
Presence of Nox:-
Figure 4.2:-A sector view of the Open-w piston
Cut-plane videos for Open-w Piston:-
Presence of HydroCarbon:-
Presence of Carbon Monooxide (CO):-
Presence of Soot:-
Presence of Nox:-
It can be clearely observed that all the Nox, Soot & UHC emissions have lesser values in Open-w piston. For instance, Open-w has near zero hydrocarbon emissions while UHC emission is of the order of magnitude is (8e-07) at Omega Piston.
Similarly the Nox emission by Open-w piston is ten-times lesser compared to its counterpart.
However, for better understanding the graphical method is chosen to judge both the pistons.
5.Graphical Reperesentation of the Parameters Involved
For the better compariosn between the two pistons we resort to Graphical Methods.
Since, emission has already been discussed let us first start with the comparison of the emissions let out by the engine.
Presence of Hydrocarbons
Figure 5.1:- Graphical Comparison of Hydrocarbons by the Open-w & Omega Pistons
It can be seen from the above graph that the Hydrocarbon emission in Open_w piston is far less than its omega (bowl profile counter part). This will ultimately lead to less emission and the engine can clear safetly norms such as BSIV, Euro etc. set globally.
Presence of Carbon Monooxide
Figure 5.2:- Graphical Comparison of Carbon Monooxide Emission by the Open-w & Omega Pistons
The presence of carbon monooxide is a sign of incomplete combustion. As discussed Eq.3.1 clean combustion of diesel gives only carbon-dioxide .
From the graph it can be infered that Open-w piston gives cleaner combustion.
Presence of Soot
Figure 5.3:- Graphical Comparison of Soot by the Open-w & Omega Pistons
The open-w piston emits more soot as compared to the Omega piston. However, soot can be treated using the exhaust system to be more precise the catalytic convertor.
Presence of Oxides of Nitrogen
Figure 5.4:- Graphical Comparison of Nox by the Open-w & Omega Pistons
At high temperature combustion reaction (in the range of 1200K), Nitrogen gets oxidised. In diesel engine it is very common and is an important area of research even at USA. Honeycomb structured catalytic convertor are used to reduce the oxides of nitrogen.
Heat Release Rate
Figure 5.5:-Graphical plot of Heat Release of Open-w Omega Piston
There is a large amount of fluctuation in HRR (Heat Release Rate) plots for both open-w & omega pistons. However, the area under the graph of the open-w piston vs Crank angle is higher than its omega counterpart.
Hence heat release by open-w piston is larger. Hence open-w is better piston design. For more confirmation the Integrated Heat Release is also ploted.
Integrated Heat Release Rate
As seen in this graph the integrated heat release by the open-w piston is higher.Since there is greater energy available in the open-w piston, more energy goes into the crankshaft. Hence, usage of Open-w piston over Omega is better.
6.Inference
It can be infered that Open-w piston can be instead of Omega piston for better power values (IHR & HRR) and to be within emission norms.