Assignment 4

AIM :- To simulate the model for direct injection compression ignition (IC) engine.

OBJECTIVES :-

The main objectives of this challenge are-

• To compare SI & CI and list down differences.
• To find BSFC
• To find Exhaust temperature
• To find air fuel (A/F) ratios
• To change MFB50 and observe impact on performance

THEORY & INTRODUCTIONS :-

Diesel 6 cylinder TC engine is a basic model of a Diesel engine. It demonstrates many of the objects which can be used to model a turbocharged, compression ignition engine.

The engine :-

The engine is a 4-stroke, 6 cylinder, 11.7L engine. There are three valves per cylinder (one intake, two exhaust) and fuel is injected into the cylinder. The engine runs in “speed” mode, where the engine speed is entered by the user and the engine torque is calculated. Combustion is modelled by the DI wiebe method. In-cylinder heat transfer is modeled using the Woschni method and in-cylinder wall temperature are specifiedby the user. This simulation will run untill it reaches steady state condition for three different engine speeds.

The intake system :-

The intake system starts with an ambient condition ”End Enviornment” going into a smooth “bellmouth” orifice. The orifice has been made effectively smooth by setting the forward and reverse discharge coefficient to 1.

Cetane number :-

It is an indicator of the combustion speed of diesel fuel.

CN of fuel = Percent of n-cetane + 0.15*percent of HMN

If there have larger the cetane number,

• Shorter is the ID, and
• Quicker the fuel will self ignite.

Self Ignition :-

Self ignition charecterastics of fuels. If the temperature of a fuel is raised above the self ignition temperature (SIT), the fuel is spontaneously ignite after a short ignition delay (ID) time. The higher above SIT which the fuel is heated the shorter will be ID. Ignition delay is generally on the order of thousands of a seconds.

Significance of cetane number :-

Diesel Cycle :-

Fuel Injector :-

Combustion in CI engines :-

1. Automization :- Fuel drops are break into very small droplets.
2. Vaporization :- The small droplets of liquid fuel evaporate to vapor.
3. Mixing :- After vaporization, the fuel vapor must mix with air to form a mixture.
4. Self ignition :- At about 8 deg bTDC, 6 - 8 deg after the start of injection.
5. Combustion :- It starts from self ignition simultaneously at many locations in the slightly rich zone of the fuel jet.

Rate of heat release in CI engine :-

Chemical equation :-

Polution:-

1. NOx is in-cylinder temperature dependent
2. Control In-cylinder temperature
3. Exhaust gas recircuilation
4. Control rate of fuel burning
5. Electronic fuel injection(CRDI)
6. Soot is solid carbon
7. Swirl, bowl design
8. Sufficient air avaibility
9. Turbocharging -> It is used only in CI engine.

Swirl motion :-

This motion is very important in case of diesel engine.

In-cylinder motion :-

# Difference between SI & CI :-

The main differences of SI and CI are as follows-

Also CI engine have higher efficiency as compare to SI engine. CI engine have more air fuel ratio (i.e. >=19) and SI engine have smaller air fuel ratio. Cetane number is for diesel engine while octane number is for petrol engine.

Geometry :-

I used following geometries for this challenge is as follows-

1. Model Selection :-

For doing more comparitive study and analysis I consider 6-cylinder diesel engine. The path of this model selection is as-

“File menu -> Example -> Engine 1D_gas exchange combustion -> Diesel -> Diesel_6cyl_TC.gtm”.

2. Engine model :-

The above figure shows skematic view of engine model, where we can see that turbine, compressor, exhaust and intake manifold. The whole assembly is attached to the injector controller.

3. MFB-50 :-

This is the cylinder settings, in which we consider mass flow rate. Through this MFB50 we can change the duration of combustion, mass flow rate. GT-suit takes by default 50% mass flow rate.

4. Case set up :-

Here I consider total 6 casses, according to mass flow rate. Here I want to show the effect of MFB50 on the engine combustion.

5. Run setup :-

Here I run the simulation in parellal by enabling “Automatic shut off when steady state”.

Results :-

1. Calculation status :-

Here showing the status of each case, case setup number, case label, Time, Period and CPU time.

2. Compressor/turbine/Pump/fan :-

Here showing different values of engine parts such as pressure ratio, mass flow rate, power, efficiency of compressor and Turbine. Also showing different engine speed.

3. Cylinder :-

Here showing the values such as Burned mass percent at combustion start (EGR+Resid), Effective AFR at EVO, IMEP720- net IMEP, Indicated efficiency, maximum pressure, volumetric efficiency (Manifold), Air.

4. Engine geometry :-

Here showing values of some basic components of engine.

Bore = 119mm Stroke = 175mm Connecting rod length = 300mm

IVC = -118deg EVO = 100deg IVO = 314deg EVC = 400deg

5. Engine :-

Here we can find out the values of engine speed, IMEP-720, BMEP, Volumetric efficiency of Air, volumetric efficiency(manifold) of Air.

6. Engine speed :-

Here we can show the values like Brake torque, Brake Power, BSFC, IMEP720, BMEP, PMEP, FMEP, volumetric efficiency, AFR, EGR percentage…etc.

7. Engine operating conditions :-

Here we can find the parameters like combustion start, injection start, pressure, temperature and velocity. Temperature, velocity decreases as engine speed decreases. As simulation increases pressure are increases.

8. Flow circuit :-

Here we can find out the values of average time step in angle and time, cluster name, cumilative simulation timestep, percentage of timesteps, timesteps restricted by and timesteps per cycle as shown in above snapshots.

9. Flow steady state :-

Here we can find mass flow steady state, mass flow tolerance, Maximum change, Part, Pressure steady state, pressure tollerance, temperature steady state, temperature tollerance and time as shown in above snapshots.

10. Turbos :-

Here we can shown average mass flow rate, average power, average speed, massflow average efficiency, massflow average map pressure ratio as shown in above snapshots.

11. RLT steady state :-

Here we can find out time, RLT variables, part, steady or not?, tollerance, change, target value, actual value and difference as shown in above snapshots.

12. Steady state symmetry :-

Here we can show that flow, ODE, controls, thermal and convergence RLT as shown in above snapshots.

13. Engine Performance predictions (SI):-

Here we can find out engine performance predictions parameters in SI system.

14. Engine performance predictions (US) :-

Here we can find out engine performance prdictions parameters in US system. The values are same, only the unit are changes according to acceptance.

15. Engine performance (fuel energy basis) :-

A)

B)

Here we can see that different engine speed and according to that energy(KW) and %of fuel energy with respect to fuel energy basis.

16. Key cylinder predictions :-

A)

B)

Here we can see that key cylinder prediction parameters. Different pressure, fuel and temperature values. The range of values are given below-

Volumetric efficiency = 85 - 90%, Lambada effective = 1.6 - 1.8, ISFC = 224 - 228 g/KW-hr, Intake pressure = 2.9 - 3.0 bar, Intake temperature = 335 - 345 k, Exhaust pressure = 3.3 - 3.7 bar, Exhaust temperature = 976 - 1000k, Heat transfer = 12.1 - 12.3%.

17. Engine MEP, Torque & Power :-

Here find out the values of Mean effective pressure, torque and power for different engine speed.

Plots :-

1. Burn rate :-

The graph is plotted between burn rate vs crank angle. After compressor burn rate automatically increases in vertical straight line and after small time it decreases but not upto zero value and then slightly increases and then decreases as shown in above plot. Burn rate is depends on pressure and temperature and hence at compression pressure and temperature increases due to the combustion of air fuel mixture.

2. Heat transfer rate :-

This plot showing radiation, burned and unburned fuel. After compression stroke at TDC burned rate gradually increases, the result is very low radiation and unburned fuel. After TDC heat transfer rate decreases and after intake stroke unburn fuel decreases, as shown in above plot.

3. LogP - LogV diagram :-

The graph is plotted between pressure vs volume. At intake valve open pressure is high and intake valve close pressure is lower down. Pressure is decreases from intake valve open due to temperature increases and at start of combustion prssure and volume are in middle range.

4. Temperature plot :-

At start of combustion temperature plot increases and after reach at peack point it decreases as shown in above plot. Combustion takesplace just after TDC I.e. in power stroke. At start from BDC to TDC compression takesplace and the gap between piston and cylinder decreases so pressure incraeses and combustion takesplace. At intake stroke temperature decreases upto initial temperature due to exhaust of air.

5. Compressor efficiency map :-

Where mass flow rate and pressure ratio balanced, at that point efficiency is maximum. Where maximum mass flow rate but less pressure ratio there efficiency is decreases as shown in above plot.

6. Compressor speed map :-

As corrected mass flow rate and pressure ratio increases, engine speed increases. Compressor speed is directly proportional to the mass flow rate and pressure ratio.

7. Turbine efficiency map :-

As pressure ratio increases turbine efficiency increases as shown in above plot. Turbine works on kinetic energy principle and so that engine speed increases it means turbine efficiency increases.

8. Turbine speed map :-

It also nearly similar to the turbine efficiency because, turbine efficiency is based on the engine speed. It also depends on some enviornmental parameters like pressure and temperature and hot gasses.

CONCLUSIONS :-

From above plots we can conclude that,

1. As time decreases self ignition temperature increases.
2. As slow burning octane number increases, and at fast burning cetane number increases.
3. Heat addition at constant pressure and heat rejection at constant volume takesplace. (from P-V diagram)
4. The gap between nozzle hole and tip decreases so that more air is used while combustion.
5. CO2, H2O and N2 forms when complete combustion takesplace.
6. Swirl motion is important in case of diesel engine.
7. As MFB increases Brake power, brake torque, IMEP, PMEP, FMEP, air flow rate, BSAC, fuel flow rate, Brake efficiency decreases while BSFC, volumetric ratio decreases.
8. As mass flow rate decreases and pressure ratio increases engine speed and engine efficiency increases of both compressor and turbine.

In this way, I successfully completed this project. Founded required data, plots and effect of different quantity of MFB on different output such as power, torque and efficiency.