Week 11: Project 2 - Emission characterization on a CAT3410 engine

                           EMISSION CHARACTERIZATION ON A CAT3410 ENGINE

l. OBJECTIVE

1. Analyze two-piston bowl configuration(Open-W and Omega) of CAT3410 Engine.
2. Characterize their emission (Soot, NOx, and UHC).
3. Compare the imep and power values graphically.

ll. GEOMETRY

This project will be simulating a `60^0` sector geometry for a CAT3410 diesel engine with different piston profiles. The geometries are generated using the " make engine sector surface" tool available in CONVERGE Studio. The geometric parameters of the engine are as follow:

• Bore: 0.13716 m
• Stroke: 0.1651 m
• Squish height: 0.0001 m
• Connecting Rod: 0.263 m
• Compression Ratio: 17.5
• RPM: 1600

1. Open-W Piston

2. Omega Piston

The surface geometries generated from this tool are shown below:

Sector geometries are useful in running quick simulations when there is an asymmetry in the model involved. This engine consist of 6 nozzles, hence the model can be decided into `360^o/6 = 60^o` sectors.

 

lll. CASE SETUP

Once the profiles are created, the case setup is done by importing all the input files into respective tabs.

Some of the important parameters are derived from the input files as:

Gas Simulation

The gas thermodynamic data is completed by importing the therm.dat file.

Reaction Mechanism

The reaction mechanism is set up using the mech.dat file.

Simulation Time Parameters

Boundary

Each of the boundary values for respective boundaries is input by deriving from the boundary.in file.

Regions and Initialization

Spray Modeling

Combustion Modeling

Grid

AMR

Fixed Embedding

Once the case setup is complete, all the input files are exported, simulated, and are post-processed.

lV. RESULTS

PLOTS

1. Pressure

 

2. Temperature

 The temperature difference in both piston configurations suggests that NOx emission would be higher in the Omega piston. We will dive into the inference of this plot in the NOx emissions plot separately.

3. IHR

 The integrated heat release denotes the amount of power generated from the combustion. From the given plot, a slight decrease in power is evident in the Open-W piston configuration. This can be due to factors such as:

 1. Lesser fuel to burn/ Unburnt fuel

2. Incorrect timing

3.Insuffucuent air

The latter two points probably can't occur in this setup because this is a closed system simulation and given parameters are used to test the piston configuration bowl profile alone. We need to analyze further parameters to validate our conclusions.

4. HHR

Significant Heat release rate increase, denoting might have unburnt fuel potential.

5. Hiroy Soot

 

Internal combustion engines produce soot as a result of incomplete fuel combustion, Ideally, complete combustion in a cylinder would only produce carbon dioxide and water, but no engine is completely efficient.

Because of the way that fuel is injected and ignited, soot formation occurs more commonly in diesel than in gasoline engines. Unlike gasoline where the fuel/air mixture is ignited with a spark, fuel, and air entering the diesel cylinder ignite spontaneously from the high pressure in the combustion chamber. The fuel and air mixture in diesel engines typically do not mix as thoroughly as they do in gasoline engines. This creates fuel-dense pockets that produce soot when ignited. While the majority of soot easily escapes through the exhaust, some get past the piston rings and end up in the oil.

As soot builds to abnormal levels, engine problems begin. Soot thickness oil and negatively affect viscosity, which means the engine has to work harder to start and run during cold temperatures. Soot circulation also contributes to the formation of varnish and carbon deposits throughout the engine, which can wear down valves and seals, reducing efficiency and eventually causing failure. When excessive soot collects, it forms a congealed mass known as sludge, which is the leading cause of premature failure in diesel engines.

Hence, from the plot itself, we can infer that the degree of unburnt fuel is way higher in the case of the Open-W piston than the Omega piston. Hiroy Soot is a harmful carcinogen and must be eradicated using suitable measures such as advanced three-way Catalytic convertors, or by perfecting the combustion process by reducing unburnt gaseous fuel.

 

 

6. NOx

A compression ignition (diesel) engine runs all the time with a lean air-fuel mixture, the value of the equivalence factor (`lamda`) depending on the engine's operating point (speed and torque). The reason for this is the working principle of a diesel engine: controlling load not through air mass (which is always in excess) but through fuel mass (injection time).

Since lean mixture denotes more oxygen and lesser fuel, the nitrogen present in the air is more likely to combine with excess oxygen and produce NOx. This happens under high pressure and high-temperature conditions, which are the operating conditions of a diesel engine where spontaneous ignition takes place without the need for a spark. Hence as we earlier saw the higher incylinder temperature in omega piston configuration, Nox emission is higher as a result of it.

This can be reduced using methods that lower operating temperatures in combustion chambers, including EGR (Exhaust Gas Recirculation), which allows heat transfer between flows having temperature differences and allows for some of the heat to be carried away from the combustion chamber. We can also utilize additives in the fuel itself to curtail the interaction of nitrogen with excess oxygen at the molecular level. Research is going on such methods and engineers must utilize whatever means to reduce harmful pollutants such as these from poisoning our environment

7. CO

Even with higher values during combustion, the overall output values have decreased for Omega piston regarding the CO emissions. Open-W has an even slightly higher emission in this setup.

8. UHC

Hydrocarbon emissions are composed of unburned fuels as a result of insufficient temperature which occurs near the cylinder wall. Hydrocarbons consist of thousands of species, such as alkanes, alkenes, and aromatics. They are normally stated in terms of equivalent CH4 content.

Diesel engines normally emit low levels of hydrocarbons. Diesel hydrocarbon emissions occur principally at light loads. The major source of light-load hydrocarbon emissions is lean air-fuel mixing. In lean mixtures, flame speeds may be too low for combustion to be completed during the power stroke, or combustion may not occur, and these conditions cause high hydrocarbon emissions.

In Diesel engines, the fuel type, engine adjustment, and design affect the content of hydrocarbons. Besides, HC emissions in the exhaust gas depend on irregular operating conditions. High levels of the instantaneous change in engine speed, untidy injection, excessive nozzle cavity volumes, and injector needle bounce can cause significant quantities of unburned fuel to pass into the exhaust. Unburned hydrocarbons continue to react in the exhaust if the temperature is above `600^o` C and oxygen present, so hydrocarbon emissions from the tailpipe may be significantly lower than the hydrocarbons leaving the cylinder.

 Bu considering all this, we need to also investigate how the fuel spray propagates to know what exactly is happening that produces drastic results for just different piston bowl configurations.

 9. Fuel Mass

 10. Liquid Spray Mass

 11. Spray Penetration

 From the plots given above, we can clearly see that the spray penetration length for the Open-W piston is far lower than the Omega piston, even with the same spray and nozzle configurations. There is also a loss of fuel in the combustion chamber and this is where we need to take a closer look at the reception of fuel on the respective bowl profiles.

Note: For fuel to burn, we need to have adequate mixing of oxygen and fuel in the right mixture. To burn, a substance must have access to oxygen.

Liquid gasoline will "burn slowly" because it's only the molecules at the surface of the liquid which can burn (chemically combine with oxygen). The molecules that are NOT at the surface ( at the bottom of a jar of gasoline, for example) don't have access to oxygen, so they do NOt burn.

If you vaporize gasoline or a similar fuel, now you have a different situation - the vaporized molecules are "mixed" with air, which includes oxygen molecules, so all those molecules of fuel; are in direct contact with oxygen molecules. So, when ignited, they can All burn, really quickly. We call this fast reaction, which is the same (chemically) as burning, an explosion. If vapor is too concentrated it will not explode, or even burn. The mixture is called "too rich", if you do have not enough fuel and too much oxygen, that mixture won't burn either, and is called "too lean".

Hence, the spray penetration length actually buys time for the fuel to atomize and vapourize in the high pressure and high-temperature circumstances of the engine. If there is no time for the liquid to vapourize or if it sticks along the surface of the piston due to an inaccurate angle of reception between the nozzle and the low-profile, there will be unburnt fuel that produces soot and also loss of power.

Open-W piston vs Omega piston

when both of the piston bowl profiles are set next to each other and the parcel simulation is done, we can clearly see that the angle of entry of fuel spray is incompatible with the higher elevation of the Open-W piston configuration, causing to cut short the penetration length of the spray. This would cause some liquid fuel to stick to the piston bowl itself due to surface adhesion and hence not vaporizing at the right time.

ENGINE PERFORMANCE CALCULATOR

From the values calculated in the engine performance tool, we can get:

 Open-W piston

• IMEP = 1.24 x 10^6 Pa
• Power = work/time
• RPM = 1600
• RPS = `1600/60` = 26.67
• Degrees per second: 26.67 x 360 =`9600^o`/sec
• Duration of combustion: `270.156/9600^o` = 0.028 sec
• Power P = Work/Time = 3028.53/0.028 =108.16 KW

Omega piston

 

• IMEP = 1.396 x 10^6 Pa
• Power = work/time
• RPM = 1600
• RPS = `1600/60` = 26.67
• Degrees per second: 26.67 x 360 =`9600^o`/sec
• Duration of combustion: `270.156/9600^o` = 0.028 sec
• Power P = Work/Time = 3409/0.028 =121.23 KW

While we also look at the CA10, CA50, CA90 values, they confirm our suspicions of unburnt fuel and the CA50 values also explain slow flame propagation. The CA50 value of Open-W is higher than the CA50 value of Omega piston configuration. The Ca50 value denotes the crank angle at which 50% of the fuel is burnt completely and it is the stage where flame propagation takes place. If the CA50 value is higher, then flame propagation is slow and the fuel hasn't fully vaporized, which is further inferred from the high CA90 value of Open-W (53.02) compared to Omega (27.52).

V. CONCLUSION

From the analysis performed, the Omega piston configuration has significantly higher power output and lower soot, CO, and UHC emissions. Hence, it is the most efficient of the two-piston bowl configurations and has far lesser fuel loss too. The only problem is that NOx emissions are higher in the Omega piston and that can be reduced by lowering the temperature values in the combustion chamber using methods such as Exhaust Gas Recirculation etc.