What will happen if we add petrol in diesel cars or vice-versa?

This is a very common doubt among people of all ages. Firstly, we should understand the common differences between petrol and diesel.

• Petrol has higher self-ignition temperature (246 °C), compared to diesel (210 °C)


• Petrol engines use spark plugs to ignite the petrol, whereas diesel self ignites due to the temperature and pressure created during compression ratio.


• Petrol is highly volatile compared to diesel.


• If petrol is ignited in a cylinder having a compression ratio exceeding 11:1, knocking becomes a common phenomenon.


• Diesel needs to be injected at a very high pressure (1000 bar to 2000 bar) so that it is atomized and readily burns when injected inside the combustion chamber. Petrol is injected or mixed with air at a very low pressure of 2 to 4 bar.

When petrol is added in a diesel engine:

The temperature and pressure created during compression stroke will be very high in diesel engines. This will result in self-ignition of petrol. It will lead to knocking creating loud thumping noises. It will put a lot of stress on piston and cylinder walls leading to damage.

When diesel is added in a petrol engine:

The engine won’t start simply because diesel is less volatile and will not mix with air to form a combustible mixture. Diesel has to be atomized to make sure it burns readily when injected. But the fuel injectors in petrol engines don’t develop enough pressure to atomize diesel. Hence, combustion doesn’t take place.

Why do we mix oil with gasoline in 2-stroke engines?

This is a very valid question since 4 stroke engines have a dedicated lubrication system. The reason for the lubrication oil to be mixed with gasoline is that the crankcase is used for pumping and circulating air-fuel to the combustion chamber. Therefore, the crankcase cannot have an oil sump to store the oil.

The oil is mixed with gasoline and as the combustion process takes place, the oil settles on the walls of the combustion chamber, bearings and other wearable parts. This is the simplest and cost effective way for lubrication in 2 stroke engines. But the oil might burn with gasoline and can result in blue colored exhaust smoke

Lead Acid Battery

The demand for power is rising continuously in automobiles. Starter motors, increasing number of electrical devices are demanding more input from the battery and alternator. Vehicle’s energy sources, battery and alternators face several challenges such as:

• High power demand at extreme weather conditions (at cold temperatures, electrical devices demand higher power supply).


• To have higher load capacity at low speeds.


• Smooth operation at high loads.


• Undisturbed power supply at all conditions to safety systems (ABS, Traction control, etc.)

Battery principle:

A chemical reaction between the electrodes and electrolytes generate electricity. Battery is the storage unit for the electricity and supplies it to the vehicle loads based on the demand. The supply of electricity discharges the battery; therefore it requires an external source to recharge itself. Alternator recharges the battery by supplying current.

Starter motor has the highest current consumption of all the loads, even though for a small period of time. This is due to the fact that the suction, compression and exhaust strokes provide a lot of resistance to the crank movement. Therefore, higher power supply is required to overcome the resistance and crank the engine.

Battery supplies power only under these circumstances:

• When the engine is OFF: To crank the engine and also to supply power to other electrical loads such as lighting, music, etc.


• When the engine is ON: Once the engine is cranked, alternator not even meets the power demand of the loads, but also charges the battery. When the engine is running at idling speed or lower speed, the battery must be able to supply power to the electrical devices for a brief amount of time. Also when the power demand overcomes the alternator supply capacity, the battery assists in meeting the demand.

 BATTERY OPERATION: 

The battery must have enough energy to start the engine, especially at low temperatures. When the engine is started, the battery takes the role of electrical energy storage unit to store the current produced by the alternator. This energy is used to start the engine again next time after it has been switched off.

The battery also absorbs peak voltage to protect the sensitive loads from damage. Typically, a Lead-Acid battery is used in automobiles, which is enough to meet the energy demands. A 12V battery is used in light commercial vehicles (for e.g. Cars) and 24V battery is used in heavy duty vehicles (for e.g. Trucks).

Design:

It consists of two electrodes of different materials PbO₂ (Lead peroxide) and Pb (Lead) dipped in an electrolyte solution of dilute H₂SO₄ (Sulfuric acid) of density 1.28 kg/l. Both the electrodes have different potentials when immersed in the electrolyte. The difference in potential between the electrodes is known as the cell voltage.

The PbO₂ electrode is the positive electrode (cathode) and Pb is the negative electrode (anode). The entire setup where the two electrodes are immersed in an electrolyte is known as a cell. Two or more cells arranged in a series in known as a battery. A cell generates 2V. In a 12V battery, six cells are arranged in a series.

Battery Discharge (Generation of Current):

When load is applied, electrons flow from the negative electrode (Pb) to the positive electrode (PbO₂). The flow of electrons is known as current and this current is passed to the load (for e.g. a lamp bulb placed in between the 2 electrodes starts glowing due to electron flow).



As a result of this electron flow, the bond between lead and oxygen atoms is broken. The lead at positive electrode becomes bivalent positive ions (Pb²⁺) and oxygen becomes bivalent negative ions (O^2-). The electrolyte (H₂SO₄) separate into sulfate ions (SO₄^2-) and hydrogen (H⁺). Meanwhile, the negative electrode Pb is converted into bivalent ions (Pb²⁺).

The lead (Pb²⁺) and sulfate ions (SO₄^2-) combine at both positive and negative electrodes to form lead sulfate (PbSO₄). The oxygen ions (O^2-) combine with hydrogen ions (H⁺) to form H₂O (water).

Battery Charging:

Battery charging process is the inverse of the discharging process. Current is supplied to the battery from an external source (alternator). The current flows in reverse direction, from positive electrode to the negative electrode. As the electron flows into the negative electrode, the lead sulfate (PbSO₄) molecules are broken down. As a result, the bivalent lead (Pb²⁺) is converted to Pb. The sulfate ions (SO₄^2-) are released into the electrolyte.



At the positive electrode, the lead sulfate (PbSO₄) molecules are broken down and tetravalent lead (Pb³⁺) is formed. The sulfate ions (SO₄^2-) are released into the electrolyte.

The water molecules (H₂O) in the electrolyte are broken down into H⁺ and O^2- ions. The hydrogen ions (H⁺) and sulfate ions (SO₄^2-) combine to form dilute sulfuric acid (H₂SO₄) as the original electrolyte.

At the positive electrode, the bivalent negative oxygen ions (O^2-) and tetravalent lead ions (Pb³⁺) combine to form lead peroxide (PbO₂).

Negative plate reaction:

Pb (s) + HSO₄^- (aq.) ↔ PbSO₄(s) + H⁺ (aq.) + 2e^-

Positive plate reaction:

PbO₂(s) + HSO₄^-(aq.) + 3H⁺(aq.) + 2e^- ↔ PbSO₄(s) + 2H₂O (liq.)

Total reaction:

Pb (s) + PbO₂(s) + 2 H₂SO₄ (aq.) ↔ 2 PbSO₄(s) + 2H₂O (liq.)

s- solid

aq. - aqueous

liq. - liquid

BATTERY CONSTRUCTION:

A 12 V battery consists of a series of 6 cell packs arranges in a case made of polypropylene material. Each cell pack is made of two lead plates immersed in dilute sulfuric acid. The positive and negative polarity plates are separated by a semi permeable membrane known as the separator. Even the cell terminals, connectors and plate straps are made of lead. Likewise, 5 more cell packs are arranged in a series and the top layer is sealed by a hot molding process.



Each cell pack has a vent plug which allows refilling the electrolyte when the density of electrolyte drops. It also allows the gases in the electrolyte chamber to escape.

Battery Case:

The battery case which is made of polypropylene is acid-resistant. It is provided with partitions to separate the cell packs. The case is provided with a sediment chamber below the lower edge of the cell packs. During electrochemical process, lead accumulates as sediment as a result of plate disintegration. The sediment should not be in contact with the plates in order to avoid short circuit. Therefore, the sediment is collected in the sediment chamber.

The cell packs are connected in series using cell connectors which provide a connection to the cell terminals via an opening through the cover. The positive plates are connected using plate connectors, and the same goes for negative plates. Both positive and negative plates are separated with the help of separators.

Cell Packs:

A battery’s ampere-hour (Ah) capacity can be increased by increasing the number of plates in a cell pack. More number of plates increases the overall surface area of the plates and thus Ah capacity increases. The number of negative plates is usually one more than positive plates.



The plate is nothing but grid plates made of lead with active materials pasted on them. The active material on the negative plates is made of pure lead in the form of spongy lead (Pb) and it is of metallic grey color. The active material on the positive plates is made of lead peroxide (PbO₂) which is dark brown in color.

Separators:

Separators made of polyethylene are a vital part of the battery to avoid short circuiting. The positive and negative plates should never be in direct contact. Separators should be acid resistant and have a micro-porous structure to allow ion migration.

Cell Terminals:

The plate strap of the positive plates should be connected to form the positive terminal in the first cell. The plate strap of the negative terminals in the last cell pack should be connected to form the negative terminal of the battery. As a result, terminal voltage of 12 V is available between the two terminals.

BATTERY TYPES:

Based on the grid material used for the positive and negative plates in a cell pack, a battery can be divided into 3 types:

• Maintenance requisite batteries


• Hybrid batteries


• Maintenance free batteries

Maintenance requisite batteries (lead-antimony alloy):

These types of batteries require regular maintenance to make sure that the battery performs as intended. The grid material used as plates is made of lead-antimony alloy (PbSb). Addition of antimony to lead can make the manufacturers achieve thin grid plates. It provides the strength to withstand operations at extreme conditions.

There are various disadvantages of using antimony with lead as grid plates. They are:

• Due to corrosion at positive plates, the antimony molecules are separated from the grid plates and start travelling towards the negative plate via separator and electrolyte and starts poisoning it.


• As a result of the above point, the negative plates start self-discharging at a higher pace.


• Gassing occurs at lower voltage.


• As a result of the above factors, the battery starts getting overcharged leading to increased water consumption. This as whole results in increase in the amount of antimony released.


• The self discharge of the negative plates is one of the prime reasons why starter motors don’t receive adequate current to start the engine.

Hybrid Batteries:

In hybrid type, there are two different materials used for the plates. Lead calcium (PbCa) alloy is used for negative plates and lead antimony (PbSb) alloys are used for positive plates. The positive plates are manufactured using casting process, whereas negative plates can be manufactured using simple drawing process.

Even though the maintenance required for hybrid type is less compared to the previous type, it still does not meet the extreme low water consumption demand because of the presence of antimony.

Maintenance Free Batteries:

• Lead calcium alloy (PbCa): In this type, both the plates are made of the same grid material. Lead calcium alloy (PbCa) is used as a grid material for the plates. Use of PbCa avoids the poisoning of negative plates because PbCa does not react during electrochemical process. As a result, the self discharge of negative plates can be prevented. It also means that gassing will occur at appropriate temperature. Therefore, water consumption can be kept low and overcharging can be prevented.

• Lead calcium silver alloy (PbCaAg): In a bid to withstand adverse temperatures, the battery has had a recent development in the alloy used for the grid of positive plates. A small proportion of silver is added to the PbCa alloy and it has proven to be reliable even at higher temperatures.

Starter Motor

Before an internal combustion engine can start running and generate power on its own, it requires an external source to make it start running. This work is done by a starter motor. Starter motor provides a certain degree of momentum till the engine generates enough torque in the power stroke to overcome the resistance during suction, compression and exhaust strokes. It requires a large amount of force to start an engine.

STARTER MOTOR DESIGN:

Most of the vehicles today use a reduction gear type starter motor.

Starter Solenoid:

 Starter solenoid has 2 main functions:

• To move the pinion gear outwards so that it can mesh with the ring gear


• To complete the starter motor’s primary electric circuit

The solenoid housing consists of a solenoid switch or armature which is movable. There are 2 solenoid windings, named as pull-in winding and hold-in winding. The solenoid switch moves towards the solenoid core, pressed against the return spring. The movable solenoid switch is connected to a contact plate at one end, pressed against the contact spring. The contact plate when comes in contact with the contact switches, completes the starter primary circuit.


                                       
                                                       Solenoid Switch

The solenoid coil consists of a pull-in winding and a hold-in winding. The magnetic force in the pull-in winding pulls the armature towards the solenoid core. The magnetic pull in the pull-in winding should be high enough to close the air gap between armature and the core. Once the air gap is closed enough, the magnetic force in the pull-in winding is sufficient to hold the armature, and thus the contact plate comes in contact with the contact switches and the primary circuit is completed.

Stator Housing:

 The stator housing consists of a 6 pole permanent magnet which acts as a stator. The armature rotates inside the housing as the rotor. The drive from armature is not directly given to the pinion. A reduction gear assembly having 3 planetary gears takes the drive from the armature. The reduction gears provide high starting torque required to start the engine.

                                 
                                                      4 pole stator

The current is transferred from the solenoid switch to the armature via four carbon brushes (two positive and two negative). The armature has a laminated core which is press fitted into the armature shaft. The laminated core has slots along the circumference in which copper wire is fitted. The copper wires are connected to each other in a specific pattern and are welded to the commutator plate. The entire setup is known as armature winding.

The current flows through the carbon brushes which are in sliding contact with the commutator. Due to the rotation of the armature, the current is passed to the individual commutator plates in sequence.



The circuit in the armature winding is arranged in such a way that the current flowing in the copper wires adjacent to the north poles of the magnetic field created by permanent magnets, always flow towards the pinion. Whereas the current in the wires adjacent to south poles, flow in opposite direction (towards the commutator). Since the armature is rotating, the commutator reverses the flow in wires as different commutator plates come in contact with the carbon brushes in a sequence.



The flow of current through the armature which is placed in a magnetic field produces a force which rotates the armature. The commutator maintains the torque in the armature. The rotational force or torque is proportional to the current flowing through the armature, the strength of the magnetic field, length of the laminated core, and the diameter of the armature.

Reduction Gear Assembly:

 In a direct drive mechanism, the drive from the armature is directly given to the one way clutch and pinion assembly. In case of cold starting, the engine requires more torque to be started. Therefore, the starter motor size has to be increased to meet the high torque demand.

                  

A reduction gear assembly can achieve higher torque without having to increase the size of the starter motor. A planetary gear assembly acts as the reduction gear. Gear ratios can be varied from 3.4:1 to 6:1 based on the torque requirements. Warm starting engines can start on higher transmission ratio, and cold starting engines require lower transmission ratio.

The planetary gear assembly has a sun gear (drive gear) which is attached to the armature shaft. It has 3 planet gears engaged between the outer gear with internal teeth and sun gear. The outer gear transfers the drive to the pinion.

Overrunning Clutch:

 Overrunning clutch is also known as one-way clutch. It is positioned between the armature and pinion. Its task is to disengage the pinion from the pinion drive shaft as soon as the ring gear starts rotating at a higher speed compared to the pinion. Therefore, one way clutches prevent the armature from over acceleration once the engine has started.

Roller type overrunning clutch is commonly used for commercial vehicle application. It has a clutch shell with roller race. The roller race has cylindrical rollers which are pressed into a constricted space with the help of springs. The clutch shell drives the pinion due to a helical linkage between the shell and pinion shaft.

When the overrunning clutch is at rest, the cylindrical rollers are pressed into the constricted space between the roller race and clutch shell. As a result of this, the rollers are jammed and thus the drive from the armature is given to the pinion. The pinion is forced to rotate when the rollers are jammed.

As soon as the ring gear starts to rotate at a higher speed, it will make the pinion to overrun. At this time, the rollers are pushed to the broader side of the roller race due to friction between pinion shaft and the rollers. Now the pinion is disengaged from the pinion shaft.

STARTER MOTOR OPERATION:

The starter motor starts an engine by engaging its pinion gear with the ring gear, which in turn is meshed with the flywheel. In a typical starter motor, the pinion gear has 10 teeth. The ring gear has around 130 teeth.

When the ignition key is pressed, the ignition switch completes the circuit and current from the battery flows to the starter motor solenoid. Magnetic field is created in the solenoid winding due to electromagnetism. The solenoid winding pulls the solenoid armature, thereby operating the engaging lever which engages the pinion with the ring gear.



Under ideal circumstances, the teeth of the pinion would mesh with the teeth of the ring gear. But in most cases, the teeth of both the gears would collide with each other as they try to engage. In this case, the engine cannot be started as there would be no power delivered to the flywheel to rotate the crankshaft. The solenoid armature won’t be pulled in further and the circuit remains incomplete for the current to flow to the armature.

Typically the above solution can be solved by pushing the vehicle forward and this would change the position of the ring gear as the rotation of wheels will make the differential gears to rotate, then the propeller, then the transmission, then the crankshaft and finally rotating the flywheel and ring gear. The engagement is tried again by starting the ignition.

The above solution requires human effort and consumes crucial time. Manufacturers came up with a simple solution to add a meshing spring between the pinion and engaging lever. In this case, when the teeth of both gears collide, the solenoid armature will continue to move in as the meshing spring is compressed by the lever. The circuit is completed and the current flows through the armature. The armature starts rotating due to the rotational force created when a current carrying conductor is placed in a magnetic field. The drive from the armature is given to the pinion, which when rotates brings the pinion teeth to align with the gap in the ring gear teeth and they finally mesh and start the engine.

Use of a reduction gear would increase the torque and the overall size of the starter motor can be kept smaller. The overrunning clutch makes sure that the pinion disengages with the pinion drive shaft once the pinion starts overrunning.

The first car was built in what year?

In the year 1672, Ferdinand Verbiest, a Flemish Jesult missionary in China built what is claimed to be the first vehicle in the world. It was a steam powered vehicle and was built as a toy for the Kangxi emperor of China. It couldn't a driver or any passenger.

The first vehicle that was self powered was designed and built by a French national, Nicolas Joseph Cugnot in the year 1768. It was powered by a steam engine.

Francois Isaac de Rivaz, who was also a French national built the world's first car powered by an internal combustion engine fuelled by Hydrogen in 1808. He was also the inventor of Hydrogen powered internal combustion engine with electric ignition in 1807.

The world famous Motorwagen built by Karl Benz was the first automobile to be powered by a gasoline or petrol type internal combustion engine, also known as Spark Ignition (SI) engine in 1886.

In 1933, Citroen Rosalie was the first passenger car to be introduced with a diesel powered engine. Shortly after, in 1936, Mercedez Benz 260 D and Hanomag Rekord were launched.

Car Body Design (Unitized body)

Unitized body is the most commonly used frame in modern cars. It is a self supporting body built up as a single unit. It is built of hollow sheet steel parts onto which the other body panels such as the cross members, roof frame, side members, etc. are welded with the help of robots. It is also known as monocoque structure.

Uni-body construction was introduced to make the vehicle lighter, therefore resulting in higher mileage. It is also easier to manufacture unitized body and it provides more interior space for the passengers. It does not have any frame, instead it is made of tubular fore to make it rigid.



Unitized body is still not preferred for trucks and other heavy duty vehicles because of its less strength compared to ladder frames.

Spot welding technique is employed in welding and holding the parts together as a single unit. Multiple spot welds about 4000 to 5000 of it must be made along entire structure.

Strength and Rigidity:

The steel metal provides the strength, and the use of hollow pillars provides the torsional and bending rigidity to the structure. The rigidity should be high enough to withstand the elastic deformation.

Vibrations:

Irregular surface can cause excitation of the wheels and suspension which can transfer vibrations to the body. Apart from this, the engine and drive-train can impair the driving comfort. Varying the body wall thickness and use of cross sections can suppress the frequency of the body due to vibrations.

Integrity:

Continuous vibrations can cause stresses on body parts which can lead to cracks and welding failure. The engine support cross member is highly susceptible to such failures due to the vibration from the engine and transmission.

Collision:

In the event of an accident, huge amount of kinetic energy is transferred to the body. The body structure must be able to retain the structural integrity of the passenger cabin by preventing the kinetic energy to cause deformation to the vehicle interior. The exterior should be able to handle the deformation work.

Repair:

The body parts which deform after a accident must be easily replaceable. There must be a suitable access to the exterior body parts from the inside or outside to replace the panels, pillars,etc. and be bolted or welded. Repair work is difficult in unitized body structure.

Differences Between Petrol And Diesel

Both petrol (gasoline) and diesel are extracted from petroleum or crude oil. Crude oil is a mixture of aliphatic hydrocarbons of different lengths having different properties. Hydrocarbons are a chain of carbon and hydrogen linked together having certain properties. Petrol and diesel are also hydrocarbons present in the crude oil having different properties.

Each hydrocarbon has a different boiling point. Therefore, petrol and diesel can be extracted from crude oil based on their boiling points. Crude oil is boiled in oil refineries and later petrol and diesel or any other hydrocarbon chain can be separated at different temperatures. This method is called fractional distillation.

Let's look at some of the differences between petrol and diesel properties.

PETROL	DIESEL
Chemical Formula: Commonly used petrol has a chemical formula of C8H18.	Chemical Formula: Diesel has an average chemical composition of C12H23.
Density: Density of gasoline is around 737 kg/m3 at 600 F.	Density: Density of diesel is around 832 kg/m3 at 150 C.
Calorific Value: The net calorific value of gasoline is approximately 44.4 MJ/kg.	Calorific Value: The net calorific value of diesel is approximately 43.4 MJ/kg.
Auto-ignition temperature: The auto-ignition temperature of petrol is 2460 C.	Auto-ignition temperature: The auto-ignition temperature of diesel is 2100 C.
Method of ignition: Spark plugs are used in petrol engines to burn gasoline.	Method of ignition: Diesel is injected at the end of compression stroke in diesel engine. It burns automatically due to the intense pressure and temperature inside the cylinder.
Energy Content: Petrol has a lower energy content of approximately 33.7 MJ/kg.	Energy Content: Diesel has higher energy content of approximately 36.7 MJ/kg.
Boiling point: Boiling point of petrol is between 350 C to 2000 C	Boiling point: Boiling point of diesel is between 1800 C and 3600 C
Flash Point: Flash point is the lowest temperature at which enough fuel in the evaporated state is available for ignition. Flash point of gasoline is -430 C	Flash point: Flash point of diesel varies from 520 C to 950 C
Fire point: Fire point is the temperature at which enough vapours of fuel is available to burn for at least 5 seconds. Fire point of petrol is at least 10 degree higher than the flash point around -330 C	Fire point: Fire point is at least 10 degree higher than flash point around 620 C.
Combustion reaction: The combustion reaction in gasoline engine is as follows: 2 C8H18 + 25 O2 → 16 CO2 + 18  H2O	Combustion reaction: The combustion reaction in diesel engine is as follows: 4 C12H23 + 71 O2 → 48 CO2 + 46  H2O
Octane Rating: Petrol is rated by octane number. In certain cases, petrol and air mixture may auto-ignite due to the heat and pressure inside the cylinder rather than ignite from the spark plug at the specific time. This causes detonation or knocking resulting in rapid pressure rise causing damage to the engine. Octane rating expresses the level of resistance a gasoline fuel has to auto-ignition or knocking. Octane number or rating is defined as the percentage by volume of iso-octane (2,2,4- trimethylpentane) in a combustible mixture of the mixture of iso-octane  and n-heptane which have the same anti-knocking capacity as the fuel under test. Research Octane Number (RON) is used to measure the octane rating of gasoline. A standard unleaded gasoline has a octane rating of 95 RON. Gasoline of higher quality has 98 RON. A high performance gasoline engine uses gasoline of 102 RON.	Cetane Number: Cetane number is the converse of octane number. It indicates the combustion speed of diesel fuel. The higher the cetane number, the easier it is to ignite the diesel fuel. Cetane number is defined as the percentage by volume of cetane (Hexadecane) in a combustible mixture of cetane and 1-methylnapthalene which have the same ignition characteristics as that of the fuel tested. A standard diesel engine requires diesel fuel with a minimum cetane rating of 51.