ABSTRACT
Atkinson engine is the internal combustion engine. The Atkinson engine is mainly working on Otto four stroke engines with a different type of linking the piston mechanism with the crankshaft.
I am designing the Atkinson engine. Which we use for hybrid electric car, so we study hybrid electric car like what is hybrid electric and who is using Atkinson engine.
The all arrangement of levers in the Atkinson engine is cycle of piston through all four strokes in only one revolution of the main crankshaft, and that strokes will be different lengths. The design of engine eliminates a cam shaft.
In an Atkinson cycle, the power and exhaust strokes are longer than the intake and compression strokes and that starts a small initial charge, and these things allowing it to expand to a larger volume than it originally occupied and in this mechanism we have greater degree of fuel efficiency.
Hybrid electric vehicle is only use when the gas price is high or after long time gas price will be lower. This is especially when the cost of IC engine vehicle is lower than the HEV. As per this situation HEV can save money when driving condition are not constant like stop and go specially for city traffic.
Right now the Toyota, Honda, Chevrolet, Ford Company is using Atkinson cycle in Hybrid electric car.
INTRODUCTION
Hybrid electric car are primarily propelled by an internal combustion engine, just like conventional vehicles. However, they also convert energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor. The electric motor is used to assist the engine when accelerating or hill climbing and in low-speed driving conditions where internal combustion engines are least efficient.
This project on Atkinson engine which we used in hybrid electric vehicle, and I am going to design this engine but before that we study what is Atkinson engine and hybrid electric vehicle. We use CAD software to design Atkinson engine parts and then we assemble it.
Hybrids can be configured in many different ways to achieve a variety of different objectives. They combine the best features of the internal combustion engine with an electric motor and can significantly improve fuel economy without sacrificing performance or driving range. HEV may also be configured to provide electrical power to auxiliary loads such as power tools. HEVs are primarily propelled by an internal combustion engine, just like conventional vehicles.
We can use Atkinson engine in hybrid electric car so first we study about hybrid electric car and how does the Atkinson engine work in hybrid electric car.
INTERNAL COMBUSTION ENGINE AND HYBRID ENGINE
The internal combustion engine is an engine in which the combustion in engine by the combustion of fuel occurs with an air in a combustion chamber. In an internal combustion engine the expansion of fuel at high-temperature and pressure, and gases produced by combustion and that is directly effect on piston. This force moves the linkage and transfer in mechanical energy.
In an internal combustion engine, fuel is pumped from the storage tank to the engine, where it is injected into the cylinders. Air is then allowed into the cylinder and the fuel/air mixture is compressed by the piston. At a certain point, the spark plug ignites the mixture, and small explosion forces the piston back to the top of the cylinder. A rod connects the piston to the crankshaft where the linear energy of the piston is converted to rotational energy. This energy is sent through the torque converter to the transmission. After passing through the transmission, the energy is sent to the axle, where it passes through the differential and to the wheels. And finally the car is moving.
In hybrid electric cars, HEV have an internal combustion engine, only it is much smaller than that in a conventional car. The main purpose of the engine is that the generator provides the power for battery arrangement, and the battery is charged, electricity is supplied to a powerful electric motor that drives the transmission and is used to propel the vehicle. Under speeds of approximately 15 miles per hour, it is possible to use only power from the batteries to move the vehicle. At higher speeds, the internal combustion engine restarts and provides power to ensure that the battery is charged at all times and provide direct power to the electric motor.
A vehicle is the cycling on and off of the combustion engine in the hybrid electric system. This is what allows for the great difference in gas mileage.
TYPE OF HYBRID ELECTRIC VEHICLE
SERIES HYBRID ELECTRIC VEHICLE
In the series HEV the accessory power unit is the main energy storage system usually batteries storage energy is use by the main propulsion. The power flows from the accessory power unit to the battery propulsion system on that basis the vehicle overall performance determined and the main propulsion system, energy storage system characteristics and energy storage system is also important for vehicle performance.
The series HEV is usually simple to control because accessory power unit does not mechanically couple with the drive shaft. Since the accessory power unit is not mechanically coupled to the drive system it can operate at a constant speed where it is most efficient, where extending the range of vehicle, and produce the least amount of emission.
In the series system we can see accessory power unit is very important which is joining with battery and transfer power to battery. There are to motor in series system and that is connected mechanically with system. Power comes through engine to the motor and that motor electrically connected with the battery and one motor mechanically connected with the axel. Accessory
Accessory power unit
SERIES HYBRID VEHICLE
B. PARALLEL HYBRID ELECTRIC VEHICLE
In the parallel hybrid vehicle the accessory power unit is mechanically connect with electric drive system. This is usually mechanically complicated and involves a complicated control structure for the system. The overall propulsion system consider as a power assist, when compared to the series configuration where the overall system called range extender.
In series system battery connected with the motor and that motor connected with the engine so it's very easy system and motor through the engine is connected with the mechanically and motor through battery with electric.
Accessory power unit
PARALLEL HYBRID VEHICLE
WHAT IS ATKINSON ENGINE
As per the diesel and spark ignition internal combustion engine currently used, there is one more type of engine that was introduced hundred years ago which is now use as a hybrid electric application. The Atkinson engine separates from another combustion engine where efficiency is worked on power.
In modern application in electric hybrid vehicle the low power is compensated by the electric motor.
Engine Cycle
This engine was invented by James Atkinson in 1882 and same as many of the internal combustion engines operating in a four stroke cycle it allows intake, compression, power and exhaust strokes. And in the Atkinson engine also four strokes occur on one crankshaft operation. This is why to the different crankshaft design that allows an expansion ratio to be different forms the compression ratio. The all links of the crankshaft is adjusted which allows a longer power stroke than the compression stroke. That's why engine can achieve greater efficiency.
The Four Stroke Engine Design
In the Atkinson cycle, the compression ratio is reduced but the expansion ration is not changed for making the compression ratio smaller than the expansion ratio. The main concept of engine is to build the pressure in combustion chamber at the end of power strike and all available energy will be obtained from the combustion process. And since the expansion ratio is greater than the compression ratio, more energy from heat could be converted to mechanical energy. This makes the engine more efficient and faster.
AUTO CAD MODEL SIMPLE ATKINSON ENGINE
USING ATKINSON CYCLE IN HYBRID ELECTRIC CAR
As per the original Atkinson-cycle engine is nothing but the complex-lever system that rotated the crankshaft was more prone the failure, and the increase in friction losses. The main benefits of the engine is that increased efficiency.
Some engines in today's modern cars using hybrids like the Ford Escape and Fusion models, as well as the Toyota Prius and Lexus RX 450 models, use the Atkinson-cycle engine. In Mazda car now a days they used Atkinson-cycle engine operates in stark similarity to the Miller-cycle engine.
The modern-day Atkinson-cycle engine is much more similar to the Otto-cycle engine in that it turns its crankshaft twice in one 4-stroke cycle, and it also delays its intake-valve timing in the same way a Miller-cycle engine. Thus, it looks like a Miller-cycle engine.
A Miller-cycle engine delays its intake-valve timing to reduce the load on the piston as it rises to begin the compression stroke. It can still make horsepower by way of the supercharger, which compresses the air for the engine. A modern-day Atkinson-cycle engine, delays its intake-valve timing simply to cause the compression stroke to be shorter than the power stroke, thus the same efficiency got as per original Atkinson-cycle engine.
Now a day's Atkinson-cycle engine pushes some of its intake air back out of the cylinder, and it does without from a supercharger. That why it would make a less horsepower and since the engine moves less air at lower speeds, the low torque would be appearing.
Now, the Atkinson-cycle engine in some of the hybrid models sold in the US has a trick up their sleeves. Their electric motors that make them hybrids make their maximum torque figures at 0 rpm. The electric motor moves the car sufficiently when the efficient-but-powerless Atkinson-cycle engine cannot do that.
The Atkinson currently in use for electric hybrid cars are in modified version. The low power of the engine is compensated by the electric motor. When the engine is running in high power, the extra power is supplemented by the motor. These motors can either be used independently or in combination with the Atkinson cycle engine. Together the desired fuel efficiency is achieved without the loss of power.
WHAT IS ROTARY ATKINSON ENGINE
The engine consists of two interlaced circular chambers of slightly different diameters. Inside these chambers revolve two rotors about separate centers. Each rotor is located by its own bearings. The rotors do not rely on casing contact for their location as in a Wankel engine. Sealing of the rotors against the chamber walls is excellent because of their circular orbits and large sealing surfaces. The expansion of the engine is uniform. It does not have a hot and a cold side like the Wankel. Thus the engine does not require high tolerance manufacturing and wear of the rotors is not a factor. Induction air enters at the centre of the engine and compression and expansion occurs at the periphery producing uniform heat flow characteristics. Each chamber within the engine is entirely separated from the others. This allows for the future development of alternative fuels like hydrogen to be used without the valve overlap and sealing problems associated with piston engines.
The engine does not have a traditional Otto or Diesel cycle. There are two compression phases. The first compression phase, which has a low compression ratio, controls the scavenge of the exhaust gases. After the scavenge of the exhaust gases, the air is then partially re-circulated to act again in the next scavenge phase, the remainder of the air goes on to be compressed again in the second compression phase. In this second compression phase, the air is compressed at a higher compression ratio where the fuel is added. It is this fuel/air mixture that ignites to form the expansion phase. The inlet phase is in part contributed to by the scavenge gases. This all provides for an extremely efficient handling of the gases, with a significant reduction of exhaust emissions and excellent fuel economy. The expansion volume is larger than the second compression volume and this therefore increases the thermodynamic efficiency.
WORKING OF ATKINSON ENGINE
The original Atkinson-cycle engine was totally different design than either the Otto- or Miller-cycle engines. The crankshaft was mounted on a different axis than the piston rod, and was connected by a series of levers that allowed the piston to rotate the crankshaft one revolution for every 4-stroke cycle. And the Otto-cycle crankshaft rotates twice. Since the 4-stroke process occurred once each crank revolution instead of twice, the valves could be operated directly off the crankshaft, thus eliminating the need for a camshaft. But the main objective of the Atkinson-cycle engine was to make its compression stroke shorter than the power stroke, thus making the compression ratio smaller than the expansion ratio.
The thermodynamic efficiency is increased because volume for the compression and expansion stage together with an asymmetric geometry. The fuel burns at a higher temperature and pressure for a given compression ratio but the exhaust gases exit the engine cooler. Thus more energy is extracted from the fuel. The engine uses compressed air scavenges for the exhaust phase. Exhaust gases are oxidized totally therefore we reducing emissions. With one power phase per revolution, the engine produces over twice the power of a conventional engine for the same design. It is also expected that, being a rotary engine, the maximum rpm will be at least one and a half or twice that of a conventional engine. This increases the tractability of the engine like low rpm torque to high rpm power.
As per this engine is able to run like a more reversible adiabatic process, in which the heat transfer of the combustion process equals zero. When the engine compresses the air, it heats up.
When the air expands in the power stroke, it cools. Although no machine is perfect and adiabatic process is not possible perfectly, the Atkinson-cycle attempts to do so by generating less heat in the compression stroke and more heat in the power stroke because of that the efficiency of the engine increase significantly.
DESIGN ALL PARTS OF ENGINE
Fly Wheel for Engine.
2. Belt
Cylinder
Piston
Gear Pulley
Cam
Connecting Rod 1
Connecting rod 2
Small cam
Cylinder Head
ASSEMBLY OF ATKINSON ENGINE IN CAD
RE - DESIGN CONCLUSION AND BOM
This is the calculation for re-design engine and how can we get more efficiency so I calculate some losses for this design. I can use E85 fuel for engine and engine is 2.0 L, 8kw motor, speed manual transmission, 336V/60kw battery and rear traction motor.
Calculating Fuel use:
Eng_pwr_out = Eng_spd* (π/30)*Eng_trq
Where torque in NM, Speed in RPM and Power in Kw
Now we assume that if required torque was 80Nm at 2000 rpm and the engine efficiency was 27.8%, then the required engine power would be
Eng_pwr_out = 2000* (π/30)*80 =16.8KW
Eng_Fuel_ use = 16.8 KW/0.287= 60.3 KW
Calculating battery losses:
Losses are calculated as I²R. Where I is battery current and R is the charge or discharge resistance. By this equation Open circuit voltage of the battery (Voc), power (p), and resistance(R) to calculate current I
Pideal = I*Voc
Ploss = I² *R
Which can arrange quadratic equation to solve current?
R*I² -Voc*I + P = 0
I= Voc- Voc² - 4RP/2R
Calculating generate losses:
BAS : belt alternative starter efficiency
BAS_Mech_pwr = Eng_spd*ratio*(π/30)*trq
This time the load is 20Nm and the additional torque load on the engine is 40 Nm, so speed is double as per double torque on engine is 120 Nm.
Eng_Pwr_out = 2000*(π/30)*120 = 25.1 Kw
Eng_fuel_use = 25.1Kw/0.307 = 81.9 Kw
Now, BAS_Mech_pwr = 2000*2*(π/30)* -20 = - 8.38 kW
BAS_Elec_pwr = -8.38*0.819 = -7.53 kW
Now the amount of power that is stored in the battery can be calculated
I = 364 - 364²-4*0.378*-7500 / 2*0.378 = -20.2 A
Ploss = (-20.2)² *0.378 = 154 W
Pstored =-7.53 +0.154 = -7.38 KW
ESS_eff = -7.38/-7.53 = 98.0%
80 Nm to transmission
120Nm Engine
BAS
-20 Nm*2
ESS
Engine efficiency = 30.7%
Engine Power = 25.1 Kw
Engine Fuel use = 81.9 Kw
Engine Power Loss = 56.8 Kw
BAS eff = 89.9 %
BAS Mech Power = -8.38Kw
BAS Elec Power = -7.53 Kw
BAS Power Loss = 0.84 Kw
ESS eff = 98 %
ESS Power = -7.38 Kw
Power Loss = 0.15 Kw
Calculate Conversion Efficiency:
Conversion efficiency = ESS Power Stored/Δ Engine Fuel
= Pstored/(Engine Only Fuel- Engine generate Fuel)
So Conversation _eff = -7.38/(60.3 - 81.9) = 34.2%
Conversation efficiency for some engine and BAS speed and net output torque equal to 10 NM
Net Torque (Nm)
Engine speed (rpm) and BAS speed/2(rpm)
1000
1500
2000
2500
3000
10
40.4%
39.5%
48.7%
40.6%
37.4%
20
34.9%
38.7%
38.9%
34.0%
39.8%
30
33.3%
35.3%
31.8%
35.2%
34.8%
40
31.6%
32.2%
33.2%
32.7%
33.4%
50
31.1%
32.0%
36.1%
32.7%
36.3%
60
27.8%
32.0%
35.0%
35.7%
37.9%
70
28.1%
33.8%
32.2%
39.1%
34.4%
80
33.1%
31.9%
32.4%
36.1%
32.2%
90
28.7%
31.7%
34.1%
34.3%
33.6%
100
24.6%
35.6%
34.8%
32.9%
35.5%
BILL OF MATERIAL
SR. NO.
DESCRIPTION
PROCESS
QTY
1
FLY WHEEL
1
2
SHAFT
2
3
CAM
1
4
SMALL CAM
2
5
PISTON
1
6
CYLINDER
1
7
CONECTING ROD
3
8
BASE PLATE
1
9
CYLINDER SUPPORT
1
10
CYLINDER HEAD
1
11
SPARK PLUG
1
12
BELT
1
13
GEAR PULLEY
2
14
FLYWHEEL SHAFT SUPPORT
2
15
CONNECTING PIN
4
16
CONNECTING ROD SUPPORT
1
APPLICATION OF ATKINSON ENGINE
Powerful small size, low weight, i.e. airplane, motorcycles, performance cars etc.
Hybrid power or generating situations
High efficiency applications
Alternative or multiple fuel uses (including hydrogen)
High tractability (low rpm torque to high rpm power)
Low vibration, i.e. small vehicles or hand tools (petrol or gas) etc.
Low noise situations
Hyundai Sonata Hybrid (front-wheel drive)
Toyota Prius hybrid electric (front-wheel drive) with a (purely geometric) compression ratio of 13.0:1
Ford Escape/Mercury Mariner/Mazda Tribute hybrid electric (front- and four-wheel drive) with a compression ratio of 12.4:1
Ford Fusion Hybrid/Mercury Milan Hybrid hybrid electric (front-wheel drive) with a compression ratio of 12.3:1
Toyota Camry Hybrid hybrid electric (front-wheel drive) with a compression ratio of 12.5:1
Chevrolet Tahoe Hybrid hybrid electric (four-wheel drive) with a compression ratio of 10.8:1
Lexus RX 450h hybrid electric (front-wheel drive)
Mercedes ML450 Hybrid (four-wheel drive) hybrid electric
Mercedes S400 Blue Hybrid (rear-wheel drive) hybrid electric
Lexus HS250h (front-wheel drive)
Infiniti M35h Hybrid (Rear-wheel drive)
Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at bottom dead centre and top dead centre. The effective compression ratio of the air-fuel mixture in an Atkinson cycle engine, with respect to atmospheric pressure, is lower due to the aforementioned delay in closing the intake valve.
ADVANTAGE OF HEV ENGINE OVER OTHER ENGINE
1. Gas mileage by vehicle
HEV
ICEV
Car
Gas Mileage (miles per gallon)
Car
Gas Mileage (miles per gallon)
Prius
50
Corolla
29
Insight
41
Civic
29
Malibu Hybrid
30
Cobalt
29
Fusion Hybrid
39
Focus
30
As compare to cost level HEV is more efficient and less cost as compare to icec engine
Extremely compact
Uncomplicated design
High power and torque
Minimal vibration
High RPM
High fuel efficiency
Low Emissions
Reduced number of components
High thermodynamic efficiency
Multiple Fuel capability
Very flexible internal geometry
Noise Reduction
CONCLUSION
