Changes in Engines from BS-IV to BS-VI

1. Introduction to Combustion in Automobile

Internal combustion (IC) engines are widely used in automobiles and machines for power generation
The power is generated by combustion of air and fuel in the engine cylinder. The high pressure and temperature gas pushes the cylinder and the power is transferred to wheel through a transmission system.
Combustion of a fuel occurs with air (oxygen) in a small combustion chamber
The combustion energy is used to drive vehicles using the power transmission systems

Four stroke engines are used due to low fuel consumption
- Intake (Suction) Stroke: Air and fuel mixture is inducted inside the cylinder
- Compression stroke: air and fuel mixture is compressed in the cylinder
- Expansion (Power) stroke: after ignition the combustion produces high pressure gases to push the piston
- Exhaust stroke: Flue gases are exhausted from the cylinder

For, petrol engine, air and fuel are mixed before combustion and the type of combustion is premixed. A spark plug is used to ignite the mixture.
However, for diesel engine, the type of combustion is non-premixed. The temperature of air inside the cylinder is enough high due to compression and fuel injected fuel burns without any external ignition source
For homogenized charge compression ignition (HCCI) the type of combustion is partially premixed. The temperature of air and fuel mixture increases due to compression and mixture burns without any external ignition source.

In a traditional petrol engine, carburetor has been widely used for mixing of petrol and air
With the help of Floating valve, the petrol is injected in the venturi (smallest cross section) of air dict
The premixed mixture of air and fuel can be controlled by throttle valve

In petrol engines, air and fuel are mixed prior to combustion. It can be treated as premixed combustion
Spark plug provides the ignition energy to burn the air and fuel mixture
Flue gases from the combustion are exhausted
These flue gases are passed through different post-combustion treatment in order to reduce the emissions such as NOx, SOx etc.

1.3 Conventional Diesel (Compression Ignition) Engines

Pollution, noise and discomfort are major issues observed in conventional combustion in IC engines
Lack of filter to collect the particulate matters
Major reasons are incomplete mixing of fuel, lack of sufficient time of combustion and high temperature of flue gases

Due to collection of unburned (hydrocarbon) particles in the exhaust pipe mixes with surrounding air. This can lead to back fires in bikes

There are various types of emissions from petrol and diesel engines such unburnt hydrocarbon, carbon monoxide, NOx and SOX
These emissions can results in the formation of smog in atmosphere
It is essential to control or minimize the unwanted emissions by adapting fuel efficient and eco-friendly combustion technologies

Emission levels are defined in the Pollution Emission Norms by government of India
With an increase in environmental adverse effect, the emission level of all harmful gases have been reduced
To reduce the emissions,combustion and exhaust systems of IC engine have been modified as per type of combustion (SI or CI) and fuels
As per the following table, the emission levels are decreased from BS4 to BS6 engines.
For both petrol and diesel engines, the NOx level is drastically reduced
Particulate matter and unburnt hydrocarbon emissions are reduced in BS6 engines

Noways, various mechanisms have been deployed with combustion chamber in order to reduce emissions such as programmer controlled fuel injector, exhaust emission reduction using selective catalytic converter and particulate traps
The NOx formed in IC engine is allowed to pass through selective catalytic reduction )

The SCR unit is placed in exhaust duct before the silencer. This is commonly used in most BS-VI bikes
The amount of ammonia or urea injection into the SCR unit depends on the level of NOx formation

For four wheelar, the SCR unit and muffler are also placed in exhaust duct before the silencer to reduce particulate matters and emissions.
To provide the accurate air fuel mixture ratio, many modern combustion controlling techniques have been implemented in many cars and truck such as MPFI, CRDI, CRDI VCR, GDI, etc. These methods ensure fuel efficient combustion.
Exhaust systems are significantly modified with EGR (exhaust gas re-circulation), Advanced catalytic converters, SCR( selective catalyst reduction), Urea after treatment devices and particulate filters

The following parts have been improved or added for complete combustion of hydrocarbon, reduction of NOx and particulate matters

Modification in exhaust system
Introduction of DPF (Diesel Particulate Filter) in order to reduce the soot emitted from diesel engines.
Reduction the Sulfur content in the exhaust which makes more cleaner
SCR (Selective Catalytic Reduction) in exhaust system to reduce NOx level