Shaping the Future

Emissions Formation and

Control

Formation and In-Cylinder Control Prevention is better than cure ! (and its cheaper )

Consider formation and in-cylinder control for; Carbon Monoxide (CO) Hydrocarbons (NMOG) Nitrogen Oxides (NOx) Particulates

Formation and In-Cylinder Control Prevention is better than cure ! (and its cheaper )

Consider formation and in-cylinder control for; Carbon Monoxide (CO) Hydrocarbons (NMOG) Nitrogen Oxides (NOx) Particulates

CO Formation & In-Cylinder Reduction

Produced through incomplete combustion

Affected by ;

oxygen starvation (rich mixtures)

fuel vapourisation rates;

poor injection quality

low ambient temperatures

Not a significant concern for diesel applications and other lean burn systems

Formation and In-Cylinder Control Prevention is better than cure ! (and its cheaper )

Consider formation and in-cylinder control for; Carbon Monoxide (CO) Hydrocarbons (NMOG) Nitrogen Oxides (NOx) Particulates

HC Formation & In-Cylinder Reduction

Pre Ignition HC Formation

Excess air and excess fuel can result in very slow flame speeds or no ignition

Large (cold) surface areas can cause flame quenching

HC Formation & In-Cylinder Reduction

Post Ignition HC Formation

Local pyrolysis of the fuel will prevent vapourisation

Slow air-fuel mixing results in local over-rich mixtures

In-Cylinder Spatial and Oil Distribution Effects

HC Formation & In-Cylinder Reduction

In-Cylinder Spatial Effects - Crevices

HC Formation & In-Cylinder Reduction

In-Cylinder Spatial Effects - Crevices

HC Formation & In-Cylinder Reduction

Air Fuel Ratio

HC Formation & In-Cylinder Reduction

Equivalence Ratio

Rich (Excess Fuel)Lean (Excess Air)

High air-fuel ratio (reduced equivalence ratio) for example during transient accelerations reduces laminar (and hence turbulent) flame speeds causing unstable combustion (high COV of IMEP) and increased HC (HC Tail)

HC within wall quench layer increased by the presence of surface deposits (more traps) – less HC from a new engine

Oil layer absorbs HC during compression and combustion and release during exhaust

Blow down turbulence ejects HC from port area

HC scraped off cylinder walls during exhaust stroke

Coldest gas (highest HC) ejected at the end of the stroke

Time Dependence

HC Formation & In-Cylinder Reduction In-Cylinder Spatial and Oil Distribution Effects

In-Cylinder HC Reduction ;

Good transient Air-Fuel Ratio control

Good combustion chamber design to improve Air-Fuel Ratio excursion tolerance

Minimising crevice volumes

Minimising surface areas (chamber & port surfaces)

Minimising oil and other deposits

High coolant and chamber wall temperatures (good warm up)

Optimum fuel preparation – no large droplets (min sac volumes)

HC Formation & In-Cylinder Reduction

Formation and In-Cylinder Control Prevention is better than cure ! (and its cheaper )

Consider formation and in-cylinder control for; Carbon Monoxide (CO) Hydrocarbons (NMOG) Nitrogen Oxides (NOx) Particulates

NOx Formation & In-Cylinder Reduction

Nitrogen from the air is oxidised during the combustion process. There are six oxides of nitrogen:

Important Unimportant

nitric oxide NO nitrogen sesquioxide N2O3

nitrogen dioxide NO2 dinitrogen tetroxide N2O4

nitrous oxide N2O dinitrogen pentoxide N2O5 (s)

Fortunately only NO, NO2 and N2O are important in the automotive industry. Only NO and NO2 are regulated as NOx

Nitric Oxide is the predominant oxide in exhaust gas:

gasoline engines NO2/NO <2%diesel engines NO2/NO 10-20%

NO concentration can be predicted with reasonable accuracy using chemical rate kinetics;

Reaction rate constants for the forward (f) and reverse (r) directions are available so enabling the rate of NO formation to be given by (Zeldovich)

The rate ‘constants’ are highly temperature dependent ~ NOx formation is very much dependent on combustion temperature

NOx Formation & In-Cylinder Reduction

NOx Formation & In-Cylinder Reduction NOx is formed at peak combustion temperatures

During the expansion stroke the temperatures fall and the NO reaction chemistry ‘freezes’

The higher the peak combustion temperatures the greater the NOx

Hence strong AFR dependence…

HC

NOx Formation & In-Cylinder Reduction

Reducing peak combustion temperatures by ;

Delaying onset of combustion

Prolonging combustion

Increasing the inert charge mass (thermal sponge) through internal or external Exhaust Gas Recirculation

Reducing the compression ratio

Running lean

Most NOx reduction methods also reduce the thermal efficiency

Often an HC – NOx trade off

High Pressure

Low Pressure

EGR acts as a thermal sponge and significantly reduces NOx

Cooled EGR – higher density

NOx Formation & In-Cylinder Reduction

High EGR causes HC, fuel economy and particulates issues

NOx Formation & In-Cylinder Reduction

Particulates

Increasing the injection duration (multiple injections?) reduces NOx slightly

Similarly delaying SOI

Both adversely affect Specific Fuel Consumption and HC

NOx Formation & In-Cylinder Reduction

Formation and In-Cylinder Control Prevention is better than cure ! (and its cheaper )

Consider formation and in-cylinder control for; Carbon Monoxide (CO) Hydrocarbons (NMOG) Nitrogen Oxides (NOx) Particulates

A collection of solid largely carbon particles (primary particles or spherule) often ‘stuck’ together with semi liquid matter

Ref Eastwood et al

Big particles are many spherules stuck together,

not bigger spherules

Primary Particle Formation

Transportation & Evolution

Deposition

Destruction

Particulate Formation

Particulate Formation

Particulate Composition of Diesel Engine Exhaust

Particulate

Soluble (Volatile) Fraction

InSoluble (Non Volatile) Fraction

Sulphates OrganicsInorganics

(Ash)Carbon Nitrates

4-5 Ring Poly Aromatic HC Rings

The Primary Particle (Spherule)

EGR significantly increases primary particle sizes under most engine speed & load conditions

The Primary Particle (Spherule)

Particulate Size Evolution

Particulate - NOx Trade Off

Effect of Start of Injection (SOI)

Thank You for Listening