Run Flat Tires

Run flat tires are tires that can run even after it’s punctured. These tires are specifically designed to run for a short duration after it is punctured so that you get enough time to run the vehicle to an auto repair shop.

Run flat tires are becoming more common in everyday cars. Goodyear started manufacturing run flat tires for NASCAR cars in 1966. It was introduced in the mid-1980s specifically for commercial purpose. As the technology proved its usefulness, most of the standard car models are equipped with such tires.

Run flat tires can run for about 80 km after it suffers a punctured wound. This grace period allows the driver to drive the car to his garage or repair shop.

Types of Run Flat Tires:

There are 2 types of run flat tires:

·         Self supporting type

·         Support ring type

Self Supporting System:

In a self supporting type, the tire features a reinforced side wall construction that will continue supporting the wheels in the event of air pressure loss. This design helps to operate the tires even after loss of air from the tires for the specified distance.

Support Ring System:

In a support ring system, a ring of hard rubber is provided within the tire to support the weight of the vehicle in the event of air loss.

Tire Pressure Monitoring System (TPMS):

Vehicles employing run flat tires are installed with tire pressure monitoring system to monitor pressure losses in the tires. Drivers might be unaware that their vehicle’s tires are punctured in the case of run flat tires. TPMS alerts the driver of any pressure losses in the tires.

Advantages of Run Flat Tires:

·         We don’t have to change the tires in dangerous situations. If there is a tire burst while driving on a highway, we don’t have to immediately stop and change the tires. An average run flat tire can run up to 80 km after tire burst.

·         It provides better control over the vehicle. In a conventional tire burst, drivers might panic and lose control which can be hazardous.

Disadvantages of Run Flat Tires:

·         It is expensive than a normal tire.

·         The driving experience is not comfortable. Since run flat tires are stiff, they tend to provide a harsh ride.

·         There is no wide range of specialized tread types in run flat tires. Tires especially for off road experience have not been specifically designed.

K-Jetronic Fuel Injection System

K-Jetronic is a mechanically and hydraulically operated fuel injection pump, introduced by BOSCH GmbH in the year 1973. The K-Jetronic pump requires no form of drive and one of its features is that it can meter the fuel as a function of the intake air quantity. The letter ‘K’ stands for continuous in German. Therefore, K-Jetronic pumps continuously inject the fuel in the intake ports of the engine.

 It can optimize the air-fuel mixture formation at different operating conditions such as starting and driving performance, power output and exhaust composition.

The 3 main functional areas of a K-Jetronic are:

·         Air-flow measurement

·         Fuel supply

·         Fuel metering

The air-flow is controlled by a throttle valve and it can be measured with the help of an air-flow sensor.

The fuel supply is controlled with the help of an electric pump. The pump delivers the fuel to the fuel distributor via an accumulator and a filter.

Fuel metering is dependent on the position of the throttle valve. The amount of air drawn is measured by the air-flow sensor, which in turn controls the fuel quantity to be supplied to the fuel distributor.

Fuel from the fuel distributor is supplied to the injection valves, which inject the fuel over the intake valve. The air-fuel mixture is formed over the intake valve. The air-fuel mixture has to be varied according to the various operating conditions such as start, warm up, idle and full load.

The K-Jetronic system consists of injection valves which inject the fuel continuously into the intake ports where it is mixed with the air. When the intake valves open, the air-fuel mixture is drawn inside the combustion chamber.

FUEL SUPPLY SYSTEM:

The fuel supply system consists of the following parts:

·         Electric fuel pump

·         Fuel accumulator

·         Fuel filter

·         Pressure regulator

·         Fuel distributor

·         Injection Valves

Electric Fuel Pump:

The electric pump is a roller cell pump which delivers fuel from the tank to the fuel rail at a pressure of approximately 5 bar. The roller cell pump is driven by a permanent magnet electric motor.

It consists of a roller race plate which is eccentric in shape. A rotor plate with notches (4 to 6) around its circumference is placed eccentrically inside the roller race plate. Each notch is provided with a roller. The roller race plate has an inlet port and an exit port.

When the engine is switched ON, the electric motor drives the pump. The motor drives the rotor plate inside the roller race plate. Due to the eccentric shape of the race plate, the rollers in the rotor move outwards pressing against the roller race plate due to centrifugal force. The fuel is trapped between the roller and the notch in the inlet port side and as the rotor rotates towards the exit port side, the fuel is pressurized and sent out through the exit port.

A check valve before the pump ensures that the fuel doesn’t flow back to the tank.

Fuel Accumulator:

Fuel accumulator is provided to maintain the pressure in the fuel system for a certain amount of time after the engine is switched OFF. This is done in order to help in easy restarting of the engine, especially when the engine is hot.

The accumulator is divided into 2 chambers with the help of a diaphragm. One chamber acts as the fuel accumulator and the other chamber is connected to the atmosphere. When the engine is running, the fuel enters the accumulator volume and pushes the diaphragm against the spring force. The diaphragm moves until the springs halt in the spring chamber. Thus the fuel collected at this point is the maximum accumulator volume.

Fuel Filter:

Fuel filter is often a combination of a paper filter, followed by strainer. This ensures higher degree of filtration. The paper filter has an average pore size of 10 µm.

Pressure Regulator:

A pressure regulator is fitted to one end of the fuel distributor. It is used to maintain the pressure in the fuel system constant at about 5 bar. It consists of a plunger which slides in the regulator against a spring. When the fuel supplied by the fuel pump exceeds the limit, the plunger moves against the spring to open the exit port. This allows the excess fuel to return to the fuel tank and thus maintaining the pressure.

When the fuel delivery quantity is lower, the plunger shifts back closing the exit port to allow less fuel to escape to the tank. The constant shifting of the plunger maintains the pressure in the rail.

Fuel Injection Valve:

Fuel injection valve open at a given pressure and atomize the fuel and inject onto the intake valves. They have a valve needle which sit on a valve seat. When the pressure is high enough, for e.g. more than 3.5 bar, the valve needle is raised from the valve seat, thus allowing the fuel to escape. The valve needle oscillates at a high frequency when operated. This results in excellent atomization of the fuel even if it is of small quantity.

AIR-FLOW SENSOR:

The air flow sensor here works on suspended body principle. As we are aware that the air flow quantity will decide the fuel injection quantity, accurate measurements of the air flow is required. The air flow sensor is located upstream of the throttle valve. It consists of an air funnel over which a sensor plate is free to pivot.

The air flowing through the air funnel deflects the sensor plate from its zero position to a certain amount. This movement of the sensor plate is transmitted to a control plunger of the fuel distributor via a lever. The movement of the control plunger decides the quantity of fuel to be injected.

FUEL DISTRIBUTOR:

Depending on the position of the sensor plate in air flow sensor, the fuel distributor meters the sufficient quantity of fuel to be distributed to individual cylinders. The movement of the sensor plate is transmitted to a control plunger of the fuel distributor via a lever. The control plunger moves in a barrel. The barrel is provided with metering slits.

Based on the position of the control plunger in the barrel, the control plunger opens or closes the metering slits to a larger or smaller extent. For instance, if the air flow rate is high, then the control plunger will move a larger distance against the spring to open the metering slit to a greater extent. As a result, more fuel will be delivered to the injection valve.  

Related Topics:

Gasoline:

• Gasoline Fuel Injection
• L-Jetronic (Gasoline)
• Chokes in cars (Gasoline)
• Multi point fuel injection (MPFI- Gasoline)

Diesel:

• Distributor Fuel injection Pump (Diesel)
• Inline Fuel injection (Diesel)
• Common Rail Direct Injection (CRDI)

Variable Geometry Turbocharger

Variable Geometry Turbocharger (VGT) is a device that can allow the turbine to vary its aspect ratio unlike a fixed geometry turbocharger.

What is Aspect Ratio?

Aspect ratio is the ratio of different sizes of a geometric shape in different dimensions. For a rectangle, the aspect ratio is the ratio of its longer side (width) to the shorter side (height).

Aspect Ratio of a Variable Geometry Turbocharger:

For a VGT, the aspect ratio is defined as the ratio of the area for the exhaust gases to enter the turbine to the radius of the turbine. In short, it is the ratio of area of a turbine to the radius of the turbine.

In a VGT, the radius is fixed and the area can be varied by varying the angle of the vanes provided in the turbine. Hence, by varying the area, we can vary the aspect ratio of the turbine.

Advantage of varying the aspect ratio:

In a conventional turbocharger, the aspect ratio is fixed. If the aspect ratio is small, then it will be effective in producing boost pressure for an engine running at low speed, but will be unable to provide the boost pressure at higher speed. This will result in high exhaust manifold pressure, and lower power output.

Conversely, if the aspect ratio is larger, then it will be effective in producing boost pressure for an engine running at high speed, but won’t supply sufficient boost pressure at lower engine speed. This will result in turbo lag.   

What is Turbo Lag?

Turbo lag is the delay in the power generated by an engine when we press on the accelerator pedal. In other words, turbo lag is the little hesitation we feel when we press on the accelerator pedal and the engine takes a while to respond.

Turbo lag is commonly seen in engines fitted with a larger aspect ratio turbocharger. A larger aspect ratio turbocharger will start supplying adequate boost pressure only when the engine reaches a higher rpm. The time in reaching the higher rpm is the delay in providing the boost which results in turbo lag.

A variable geometry turbo will provide the best of both worlds and overcome all the problems mentioned for both the small and large aspect ratio turbos.

Design of a variable geometry turbocharger:

VGT is pretty much similar to the conventional turbocharger. The only difference is that the turbine is provided with a set of vanes arranged in a circle around the turbine. These vanes are attached to pivot points, about which the vanes can vary its angle. The vane angles are adjusted with the help of an actuator. The aspect ratio can be varied throughout the entire speed range of the engine.

Working of a Variable Geometry Turbocharger:

At Low Engine RPM:

When the engine is running at a low rpm, the vane actuator adjusts the vane angles so that the vanes are almost closed and there is very little space for the exhaust to pass through the vanes and spin the turbine.

At low engine speeds, the exhaust flow is less and slow. By closing the vanes, the exhaust flow is squeezed through the little gaps between the vanes. This helps in increasing the velocity of the exhaust flow. The high velocity exhaust then hits the turbine and spins it faster, hence providing enough boost even at low engine speed. The driver can feel the quick engine response while accelerating the vehicle.

At High Engine Speed:

At high engine speed, the exhaust flow rate is high. If the aspect ratio is kept small at high speed, the vanes cannot squeeze the huge amount of exhaust through the narrow gap and it can saturate the turbo, hence leading to power loss. Thus the vane angles are adjusted to open the vanes so as to allow more exhaust flow to increase the boost pressure.

                            

2 way Catalytic Converters

Unlike the three way catalytic converter, 2-way catalytic converters are used to reduce CO and HC gases. 2 way converters don’t eliminate or eliminate very little amount of NO_X. They are made of only oxidation catalysts (platinum (Pt) and palladium (Pd)).

It is made of honeycomb ceramic structure with a coating of alumina. A secondary coat of precious materials, platinum and palladium is applied to the structure.

The oxidation catalyst is honeycomb shaped structure made of platinum and palladium. Since, it is an oxidation reaction; the catalyst will try to attract the oxygen atoms. The CO bond is strong enough to be split by the catalyst. Thus CO molecule as a whole will be attracted towards the catalyst surface. The catalyst surface will also attract the oxygen molecules (O₂). Now, since O₂ molecules’ bonds are weaker than the CO bond, the O₂ is split into individual oxygen atoms (O). The oxygen atoms will bond with the CO molecules to form CO₂.

2CO + O₂ → 2CO₂

The hydrocarbon (HC) molecules also get treated by the oxidation catalyst. When HC molecules come in contact with the catalyst surface, they are split into hydrogen (H) and carbon (C). Both hydrogen and carbon bond with oxygen to form water vapor (H₂O) and carbon dioxide (CO₂).

C₈H₁₈ + 17O₂ → 8CO_{2 +} 18H₂O

 Or

CH₄ + 2O₂ → CO_{2 +} 2H₂O

Etc….

_{Related links:}

• Exhaust Gas Recirculation (EGR)

• Fuel Vapor Canister

• Emission norms in India

• BS 6 norms in India

• Catalytic Converter (3-way)

Catalytic Converter

There are millions of vehicles on roads today. Majority of them are run by internal combustion engines which become a major contributor to the air pollution. Especially in cities, where huge traffic is unavoidable can result in poor air quality that can affect not just the environment, but even our health.

To solve this problem, the governments of different countries around the globe have taken necessary steps to implement stricter emission norms for vehicles. Catalytic converter is one of the devices that could lessen the intensity of harmful emissions coming out of a vehicle.

What is a Catalytic Converter?

Catalytic converter is a device that converts harmful toxic emission gases from a vehicle into less harmful emission gases. The process is achieved either through oxidation or reduction. Catalytic converters can be used to treat exhaust gases of both gasoline and diesel engines.

History of Catalytic Converters:

Eugene Houdry, a French Mechanical Engineer invented catalytic converter. He was awarded a patent by the U.S. Government for his research on developing catalytic converters for a gasoline engine.

Catalytic converters were a failure then due to the presence of tetraethyl lead in gasoline. Presence of lead in gasoline poisoned the catalytic converters and disabled it from treating the exhaust gases. U.S. Government started phasing out the use of leaded gasoline in the mid-1970s because of its neurotoxicity and its degrading effect on catalytic converters. In 1996, U.S.A completely banned the use of leaded gasoline.

The first catalytic converter for production was developed by engineers such a John J. Mooney and Carl D. Keith at the Engelhard Corporation.

3-way Catalytic Converters:

A 3-way catalytic converter is used to treat the 3 main harmful gases coming out of exhaust such as the nitrogen oxides (NO_X), hydrocarbons (HC) and carbon monoxide (CO) emissions.

There are 2 different catalysts at work: one is the reduction catalyst and the other is the oxidation catalyst. The reduction catalyst is made of platinum and rhodium. The oxidation catalyst is made of platinum and palladium.

Alumina Coating:

The catalysts are in the form of thousands of micro ducts that resemble the form of a honeycomb. The gases pass through these catalyst ducts. The honeycomb structure is applied with a coat of alumina (aluminum oxide). Alumina is highly porous which greatly increases the surface area of the structure. The alumina coat carries the precious catalyst materials which help in oxidation and reduction. This design maximizes the surface area of the catalyst, thus giving it more gases to react on.

Catalytic converter is installed between exhaust pipe and muffler. It works best when it is heated and can give efficiency up to 90%. As a result, we get less harmful toxic gases from the tail pipe.

Working of a catalytic converter:

The exhaust gases from the engine are first sent through the reduction catalyst. The reduction catalyst (platinum + rhodium) will try to eliminate NO_X as much as possible.

Reaction at reduction catalyst:

When NO_X (NO or NO₂) molecules pass through the contact area, the catalyst breaks the bond between nitrogen and oxygen atoms. Since, it is a reduction reaction; the catalyst will try to get rid of oxygen atoms and would attract the nitrogen atoms. The individual oxygen atoms (O) pair up with other oxygen atoms (O) to form oxygen molecule (O₂). The nitrogen atoms (N) stick to the catalyst surface unless they find other nitrogen atoms (N) to bond with to form nitrogen molecules (N₂).

2 NO → N₂ + O₂

(or)

2 NO₂ → N₂ + 2O₂

The reduction catalyst won’t eliminate the CO and HC molecules.

Reaction at oxidation catalyst:

The oxidation catalyst is another honeycomb shaped structure made of platinum and palladium. Since, it is an oxidation reaction; the catalyst will try to attract the oxygen atoms. The CO bond is strong enough to be split by the catalyst. Thus CO molecule as a whole will be attracted towards the catalyst surface. The catalyst surface will also attract the oxygen molecules (O₂). Now, since O₂ molecules’ bonds are weaker than the CO bond, the O₂ is split into individual oxygen atoms (O). The oxygen atoms will bond with the CO molecules to form CO₂.

2CO + O₂ → 2CO₂

The hydrocarbon (HC) molecules also get treated by the oxidation catalyst. When HC molecules come in contact with the catalyst surface, they are split into hydrogen (H) and carbon (C). Both hydrogen and carbon bond with oxygen to form water vapor (H₂O) and carbon dioxide (CO₂).

C₈H₁₈ + 17O₂ → 8CO_{2 +} 18H₂O

 (or)

CH₄ + 2O₂ → CO_{2 +} 2H₂O

Etc….

Related Topics:

• Exhaust Gas Recirculation (EGR)

• Fuel Vapor Canister

• Emission norms in India

• BS 6 norms in India

• 2 way Catalytic Converter

BS 6 norms in India

The Indian Government in a bid to control the rising pollution, especially in the National Capital Region (NCR) will implement Bharat Stage- VI emission standards by April 1, 2020.

The decision comes after Supreme Court pressed the needs to implement cleaner vehicular emission norms to tap the pollution in our country.  Union Road, Transport and Highways Minister Nitin Gadkari addressed the media, saying “Pollution is a major concern in our country. The Supreme Court has also stated this issue regularly. We have decided that we will move to BS-VI norms across the country directly from BS-IV norms by April 1, 2020. This is a revolutionary decision and important to address pollution”.

The minister also urged the automobile manufacturers to support the government in this mission and that they will receive every possible support from the government. BS-VI will be the equivalent of the Euro VI norms followed in European countries and other worldwide nations.

What are BS standards?

Bharat Standards or Bharat Stage was first implemented in the year 2000 to regulate the amount of exhaust gases emitted from a vehicle. Since 2000, Indian Government has implemented various norms to match the global standards.

The ministry has already confirmed that the BS-VI norms will be the equivalent of the Euro-VI norms. The Euro-VI norms for passenger vehicles are as follows:

Euro 6 Norms for Passenger Vehicles:

Vehicle type	CO (g/km)	HC (g/km)	HC + NOX (g/km)	NOX (g/km)	PM (g/km)
Gasoline	1	0.10	-	0.06	0.005
Diesel	0.50	-	0.17	0.08	0.005

Bharat Stage norms specifications from 1st stage to 4th stage is posted in the link below:

 Emission norms in India

Emission Norms in India

What are BS standards?

Bharat Standards or Bharat Stage was first implemented in the year 2000 to regulate the amount of exhaust gases emitted from a vehicle. Since 2000, Indian Government has implemented various norms to match the global standards.

What are the main exhaust gases?

Hydrocarbons (HC), carbon monoxide (CO), nitrous oxide (NO_X) and particulate matters (PM) are the 4 main exhaust gases.

HC and CO are more prevalent in gasoline engines, whereas NO_X and PM are more prevalent in diesel engines.

BS norms specification:

1. Two and three wheelers:

BS-I norms 2000 (2 & 3 wheelers)

Vehicle type	CO (g/km)	HC (g/km)	HC + NOX (g/km)	PM (g/km)
2W (Gasoline)	2	-	2	-
3W (Gasoline)	4	-	2	-
3W (Diesel)	2.72	-	0.97	0.14

BS-II norms 2001 (2 & 3 wheelers)

Vehicle type	CO (g/km)	HC (g/km)	HC + NOX (g/km)	PM (g/km)
2W (Gasoline)	1.5	-	1.5	-
3W (Gasoline)	2.25	-	2	-
3W (Diesel)	1	-	0.85	0.10

 2.   Passenger Cars and Light Commercial Vehicles (LCV):

BS-I norms 2000

Vehicle type	CO (g/km)	HC (g/km)	HC + NOX (g/km)	PM (g/km)
Gasoline	2.72	-	0.97	-
Diesel (W ≤ 1250)	2.72	-	0.97	0.14
Diesel (W between 1250 and 1700)	5.17	-	1.40	0.19
Diesel (W > 1700)	6.90	-	1.70	0.25

W- Weight of the vehicle (kg)

BS-II norms 2001

Vehicle type	W (kg)	CO (g/km)	HC (g/km)	HC + NOX (g/km)	PM (g/km)
Gasoline (GVW ≤ 2500)	-	2.20	-	0.50	-
Gasoline (GVW > 2500)	W ≤ 1250	2.20	-	0.50	-
	1250 < W < 1700	4		0.60
	W > 1700	5		0.70
Diesel (GVW ≤ 2500)	-	1	-	0.70	0.08
Diesel (GVW > 2500)	W ≤ 1250	1	-	0.70	0.08
	1250 < W < 1700	1.25	-	1	0.12
	W > 1700	1.50	-	1.20	0.17

GVW- Gross Vehicle Weight (kg)

BS-III norms 2005

Vehicle type	W (kg)	CO (g/km)	HC (g/km)	NOX (g/km)	HC + NOX (g/km)	PM (g/km)
Gasoline (GVW ≤ 2500)	-	2.30	0.20	0.15	-	-
Gasoline (GVW > 2500)	W ≤ 1305	2.30	0.20	0.15	-	-
	1305 < W < 1760	4.17	0.25	0.18	-	-
	W > 1760	5.22	0.29	0.21	-	-
Diesel (GVW ≤ 2500)	-	0.64	-	0.50	0.56	0.05
Diesel (GVW > 2500)	W ≤ 1305	0.64	-	0.50	0.56	0.05
	1305 < W < 1760	0.80	-	0.65	0.72	0.07
	W > 1760	0.95	-	0.78	0.86	0.10

BS-IV norms 2010

Vehicle type	W (kg)	CO (g/km)	HC (g/km)	NOX (g/km)	HC + NOX (g/km)	PM (g/km)
Gasoline (GVW ≤ 2500)	-	1	0.10	0.08	-	-
Gasoline (GVW > 2500)	W ≤ 1305	1	0.10	0.08	-	-
	1305 < W < 1760	1.81	0.13	0.10	-	-
	W > 1760	2.27	0.16	0.11	-	-
Diesel (GVW ≤ 2500)	-	0.50	-	0.25	0.30	0.025
Diesel (GVW > 2500)	W ≤ 1305	0.50	-	0.25	0.30	0.025
	1305 < W < 1760	0.63	-	0.33	0.39	0.04
	W > 1760	0.74	-	0.39	0.46	0.06

Bharat stage 6 will be the equivalent of the Euro 6 norms. The link is posted below:

• BS 6 norms in India