Project 1
Aim: To develop a forward energy-based fuel consumption model of a conventional vehicle.
Objective:
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Build a Simulink model using blocks and complete the vehicle model.
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Writing scripts in MATLAB to load all the variables required for running the Simulink model.
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Tabulate the fuel economy numbers (kmpl) for UDDS and HWFET cycles.
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Plot the time trace for the engine, transmission input, transmission output, and wheel speed on one plot.
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Plot engine torque, engine power, fuel rate, and fuel consumption using subplots.
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Plot accelerator and brake pedal, gear command, vehicle desired and actual speed, and vehicle distance using subplots.
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Plot the engine operating points on the engine fuel map.
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Generate the plots for both drive cycles.
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Study of Conventional vehicle Simulink model and creates graphs.
Solution:
Conventional Vehicle:-
Conventional vehicles use an internal combustion engine fueled by gasoline or diesel to power the wheels. In this the heat engine uses the principle of heat release through combustion of a fuel with an oxidizer in a combustion chamber to create expanding gases which pushes against a piston creating forcce and torque output.
In this vehicle engine converts chemical energy stored in the fuel into heat which is used to produce useful work. Typically use fossil fuels like petroleum (petrol and diesel).
The most popular type of engine is used in this system is 4 stroke reciprocating engine. Engine in cyclinder process can be represented by ideal thermodynamic cycles such as Otto cycle, Diesel cycle. Otto cycle is a ideal cycle thet describes the cycle process for spark ignited SI engine. and the Diesel cycle is the ideal cycle thet describes the cycle process for a compression ignited CI engine.
Energy and performance of vehicle:-
In this system the power demand on the wheel need to instant supplied by the powertrain. In other word the power coming from the powertrain dictates the power demand on the wheels (as per performance viz, acceleration, speed etc is determined by it.
In tis vehicle the powertrain is consists of an engine connected to the wheels through a transmission therefore the power comes from the engine through the transmission.
Conventional Powertrain Efficiency:-
The engine generates power by converting chemical energy stored into the mechanical energy by the process of combustion. This process of energy conversion also has an efficiency and the energy input is in the form of fuel consumption.
- Instantaneous fuel consumption is given as
Where,
mf = mass flow rate in [kg]
pe = Power of engine
pt = power of transmission
nt = efficiency of transmission
ne = efficiency of engine
QLHV = it is th ecalorific value/ lower heating value of fuel.
In this system of IC engine if tge power at the wheels is zero the engine is idling and still consumes some fuel to overcome the engine drag loss and keep it spinning this is the idling fuel consumption and know as idling process. Above mentioned formula is applicable only when the wheel power is strictly power. When the wheel power is negative either th engine is disengaged and idling or the engiune is engaged and providing some engine braking due to the engine drag losses.
The engine is consuming fuel when it is idling but even for engine braking the engine might be consuming some fuel.
The fuel consumption not only depend on the power requirement at the wheels but also is required to generate power to run the various engine and vehicle accessory loads.
System Dynamics:-
It deals with the modeling of multi domain systems through the use of a unified approach based on a ordinary differential and algebraic equation describing the static and dynamic effects.
Each systems has are two generalised variables-
1] Efforts:- It is generalised force variable. ex- torque, force, voltage, heating value.
2] Flow:- It is the generalised flow/velocity variable. ex:- velocity, current, mass flow rate.
3] Power:- It is the product of the effort and flow variable. It is interchangeable between energy domains.
Energy based models- Element models:
To models the internal physical properties of the element and the losses there are basically two kinds of approach.
1] Map based models:- Elements are modeled using maps which characterized the relationship between the input and output , output and losses etc.
2] Analytical models:- Elements are modeled using physical equation that represent the internal dynamics. These are the two extremes most models are a combination of the two with some dynamics models analytically and for some using maps.
In this model We use Forward Model:-
It also known as dynamic simulation. Dynamic models are used for detailed simulations. In this model force/torque/power is the input and the vehicle state variable velocity and acceleration are outputs. The models and simulatios are more realistic due to phhysical casualty hence appropriate for control development. There is feedback loop to meet the desired vehicle state. It is mainly used to simulate a vehicle on a driving cycle to analyse the dynamic behaviour of the system helps significantly in control development.
Control Model:
The ‘Controller’ block is the brains of the vehicle, representing the electronic control units. It is based on the driver inputs, it generates desired engine torque, desired transmission gear, and desired brake torque. These inputs are fed to the ‘Powertrain’ block which represents the drivetrain of the vehicle.
- Engine Control Unit: In this control model We use an engine control unit that gives input Engine speed by creating a look-up table. in that table, we give input Maximum torque and map speed then also create a 2nd lookup table that gives input ct torque and map speed then it substracts and multiplied. the engine speed also gives to ideal control speed to integrate from this we meet the output of the engine's required torque.
- Transmission Control Unit: In this unit, we create a steady flow variable state for controlling of gears of the vehicle in ascending and descending order with respect to time, speed, and distance. and give input to this steady state is vehicle speed in m/s to mph.
- Brake Control Unit: In this calculate brake torque and then all three control signals output is given to the powertrain.
Powertrain:
The powertrain encompasses every component that converts the engine's power into movement. This includes the engine, transmission, driveshaft, differentials, axles; basically anything from the engine through to the rotating wheels.
Engine:-
In this model, we used the map-based model to model the fuel consumption of the engine. It is based on maximum Torque and minimum torque from the controller. and then it saturated torque and gives output then saturated torque and the speed map gives fuel consumption takes the speed and torque then the output goes into saturated then it's integrated.
Transmission:-
In these models, we take engine torque, and gear selector from the controller for transmission of gear ratio. The ratio is multiplied by the transmission input torque and then the transmission efficiency positive torque and negative torque give the transmission input speed. In this case, the torque converter connects the engine to the transmission it is part of the transmission. In it basically, engine dynamics are decoupled.
Differential:-
In this taking input is the transmission output then it's going to the differential ratio multiplied by the output and input torque then meets axle torque. The axle torque is lower than the transmission torque and differential ratio.
Wheels:-
In this model, we take the axle torque from the differential and the brake torque from the controller. It is substracted and multiplied by the rolling radius and velocity then we meet the tractive force from the axle and brake torque and the wheel speed is met using velocity.
Vehicle Dynamics
This takes tractive force and road load. It dictates vehicle speed based on tractive force and road load. The dynamic equation for calculating road load is
Meq(dVveh/dt) = [(ηt*λtot)/(Rw)] *Tm− [0.5*ρ*A_f*Cd*(Vveh+Vwnd) ^2+Cr*M*g*cos(θ)+M*g*sin(θ)]
where,
ρ = Air density [kg/m^3]
A_f = Frontal area [m^2]
C_d = Drag Coefficient
V_veh = velocity of vehicle [m/s^2]
V_wind = velocity of wind [m/s^2]
C_r = rolling resistance coefficient
M = mass in Kg
g = gravity.
Then we calculate and integrate we meet acceleration of the vehicle and velocity of the vehicle which means vehicle distance and vehicle speed.
Fuel economy numbers:
As we see, the fuel economy is high in HWFET compared to UDDS, it is because, in urban driving, the vehicle encounters more traffic and it has to stop for fewer distances and it consumes more fuel at the start. In HWFET, the vehicle encounters no traffic and it moves without the use of too much braking, so it will have more fuel economy number.
Fuel economy numbers:
As we see, the fuel economy is high in HWFET compared to UDDS, it is because, in urban driving, the vehicle encounters more traffic and it has to stop for fewer distances and it consumes more fuel at the start. In HWFET, the vehicle encounters no traffic and it moves without the use of too much braking, so it will have more fuel economy number.
UDDS drive cycle and HWFET drive cycle plotting vehicle characteristics time trace for engine, transmission input, transmission output, and wheel speed:
- We can see that the graph has more fluctuations in UDDS compared to the HWFET cycle.
- Braking is high in UDDS when compared to HWFET due to traffic Peak.
UDDS drive cycle and HWFET drive cycle plotting engine torque, engine power, fuel rate, and fuel consumption:
- The vehicle consumed more power in the UDDS compared to the HWFET cycle because it has too many starts and stops compared to HWFET.
- Engine torque is also high in UDDS because while starting from rest, the vehicle requires more torque to overcome static friction.
- The fuel rate is high in HWFET because the vehicle will be in continuous movement, and it consumes more fuel.
- The fuel economy will be high in HWFET compared to UDDS because there are many stops and starts in UDDS and more fuel is consumed when the vehicle is in an idle position.
UDDS drive cycle and HWFET drive cycle plotting accelerator and brake pedal, gear command, vehicle speed, and vehicle distance:
- For UDDS, the accelerator and the brake pedal have more fluctuations because of frequent starts and stops. But in HWFET, the brake pedal fluctuations are almost near the zero line as there will be no frequent stops.
- UDDS cycle mostly runs on 1st, and 2nd gears, and uses 3rd, and 4th gears very rarely as it does not achieve high speeds in that traffic. In the HWFET cycle, the vehicle mostly run on 3rd, and 4th gears as it will be moving at high speeds. It uses 1st, and 2nd gears very frequently when braking is required.
- The vehicle speeds will be high in HWFET compared to UDDS. UDDS also has more fluctuations in speed due to frequent braking.
- The distance traveled in the given time will be high in HWFET than in UDDS because of the traffic barrier in UDDS.
UDDS drive cycle and HWFET drive cycle plotting engine operating points on the engine fuel map:
- By this, it is clear that as torque decreases speed increases.
Cocnclusion:
- The fuel consumption rate is more in UDDS than in HWFET.
- The UDDS drive cycle is best for asses of fuel consumption and Pollutant emissions of vehicles in a normalized way.
- Distance traveled is more in HWEFT than in UDDS.
- We can observe that in UDDS the efficiency of the engine & fuel consumption is lost in braking & gear changing the vehicle.