Emission Control Systems
   Dispositifs de dépollution


A number of system suppliers completed the trials of emissions abatement technology (EAT) for pre- Euro 3 taxis, and demonstrated a capability to meet Euro 3 emission limits. Suppliers listed in the table are eligible to fit approved EAT to pre-Euro 3 taxis to enable these vehicles to continue to operate with a Hackney Carriage plate in London. The Public Carriage Office will inspect taxis fitted with approved EAT prior to registration.

Supplier System description Applicable cabs Contact details


Ammonia SCR system
plus DPF

Pre-Euro LTI Fairway
Euro I LTI Fairway

Systems not available commercially


ECS TaxiCat system:
EGR plus DOC

Pre-Euro Fairway
Euro I Fairway
Euro I LTI TX1
Euro 2 LTI TX1

Bob Cawdell
Cawdell Limited PO Box 6121
DE56 1WG
Email : bob@cawdellgroup.com
Tel/Fax 01332 755477
Mob 07776 225725

Motor and

Nissan re-power & STT
CleanCab system:
Engine change, addition
of turbocharger and
intercooler, STT cooled
EGR system plus DOC

Metrocab series I, II and III

London Central Cab Company Ltd.,
1, Herne Hill Road,
SE24 0AU
Web Site :- www.mdengineering.co.uk
Tel 0207 501 9998
Fax 0207 501 9777

Clean Power, Turbo
Charger, EGR and Partial
Filter addition to Ford


PEAK system : cooled
EGR plus DOC

Pre-Euro Fairway
Euro I Fairway
Euro I LTI TX1
Euro 2 LTI TX1

Mark Evans,
Partsworld Ltd., Girton Road
WS11 0EB
Web Site :- www.gmpartsworld.com
Tel 01543 431 941
Mob 07798 582 376

STT Emtec

CleanCab system:
Turbocharger, intercooler,
cooled EGR plus DOC

Pre-Euro and
Euro I Fairway

Glenn Berglund
Business Area Manager Emissions Systems
STT Emtec AB
Web Site:- www.sttemtec.com
Email:- glenn.berglund@sttemtec.com
Tel 0046 60 64 10 41
Mob 0046 70 580 6880

Van Aaken
s Ltd.

vADDERS system:

Pre-Euro Fairway
Euro I Fairway
Euro I LTI TX1
Euro 2 LTI TX1

Alex Feher
van Aaken Developments Ltd.
Telford Avenue
RG45 6XA
Web Site:- www.vanaaken.com
Tel 01344 777553 / 467801


EGR plus combined
catalyst and partial flow
filter unit

Euro I Fairway
Euro 2 LTI TX1

Mr D Davis
The Southsea Drivers Wharf
SO14 0PF
Tel 07920 058 800

Engine &
(UK) Ltd

GTEC MK-I system:
LPG Conversion with 3-
way Catalytic converter

Euro I LTI TX1
Euro 2 LTI TX1

John Lucas
Gastech Engine & Equipment (UK) Ltd
2 Bishop Place
Web Site:- www.gastechengine.com.au
Tel 029 20308653
Mob 07980240212

1. SCR - Selective Catalytic Filter: a technique for reducing oxides of nitrogen (NOx) in the vehicle exhaust by catalysis

2. DPF - Diesel Particulate Filter: a device which filters exhaust gas emissions, removing solid carbonaceous particles (soot)

3. EGR - Exhaust Gas Recirculation: a technique for introducing a portion of the vehicle exhaust gases into the engine air intake manifold to reduce NOx emissions

4. DOC - Diesel Oxidation Catalyst: a device for reducing particulate and some gaseous pollutant emissions

5. STT - STT Emtec AB, Swedish company specializing in exhaust emissions after-treatment, and in particular, NOx reduction by EGR

We describe here briefly the three emissions control systems you are most likely to find fitted on your cab, if any: The STT Emtec CleanCab™ system, the Van Aaken system and the TaxiCat system.
Of the three systems, the TaxiCat System is by far the less invasive and the less likely to develop problems!


STT Emtec´s Emission Reduction Technology, CleanCab™

The CleanCab™ system is based upon known technology as turbo charging, exhaust gas recirculation (EGR), intercooler and EGR cooling system, which will convert the existing engine to meet the latest Euro 3 emission standard.

The main features of the CleanCab™ system is improved drivability, as the engine will maintain the power, no additional operational cost and no additive required. Just fit and forget, as no extra maintenance is required, only normal vehicle service in accordance with the manufacturer's specification.

General description of the CleanCab™ system

A turbocharger is used to feed air into the engine in order to keep the air-fuel ratio at acceptable levels and optimize the combustion. The boost pressure is controlled by the main STT Emtec electronic control unit, ECU, operating a pulse width modulated valve. The ECU is also controlling the amount of exhaust gases to be recirculated by the EGR valve.

The control system is depending on the engine load, speed and temperature. The exhaust gases are cooled by an EGR cooler to reduce the exhaust gas temperature before it is mixed with the inlet air. In addition an intercooler system is added to increase the density of the compressed inlet air.

Turbocharger system

Turbo Garrett

Turbo Garrett

The purpose of turbo charging is not primary to increase engine power, but to increase Air Fuel Ratio, AFR, at intermediate to high load conditions to make it possible to use Exhaust Gas Recirculation, EGR, without significant increase in soot formation.

Intercooler system


The purpose of an intercooler is to cool down the compressed air downstream of the turbocharger. The cooled air will reduce the combustion temperature as well as NOx formation, and at the same time also increase Air Fuel Ratio, AFR, due to higher density of the compressed inlet air. Cooled inlet air will also bring down the thermal stress on the combustion components.

Exhaust Gas Recirculation, EGR, system

The purpose of Exhaust Gas Recirculation, EGR, is to introduce exhaust gas, containing CO2 and water vapor, into the combustion chamber.
As a result EGR absorbs heat from the combustion process, lowering the temperature and reducing NOx formation. The EGR system must be able to deliver the required EGR rates to reach the target of Euro 3 emissions in combination with turbo charging.

EGR cooler

The EGR-coolers purpose is to decrease the emissions of nitrogen oxides, carbon monoxide, hydrocarbons and particulates. The cooling has to be chosen carefully for optimum reduction of nitrogen oxide emissions.

Diesel Oxidation Catalyst, DOC

An oxidation catalyst is used to reduce emissions of CO and HC. It also affects the heavy hydrocarbons adsorbed on the particulates.
Depending on the amount of hydrocarbons adsorbed the total particulate matters can be reduced by 10-30 %. The performance of an oxidation catalyst is dependent on the exhaust gas temperature.

Stt Emtec clean cab system fitted to Fairway Driver

Stt Emtec intercooler

Stt Emtec turbo Garrett

Stt Emtec system


The Van Aaken system comprises an EGR valve (Exhaust Gas Recirculation valve) and a combined Diesel Particulate Filter and Diesel Oxidation Catalyst. It also includes a Van Aaken smartbox (Diesel ECU).

Van Aaken system fitted to a 1997 Fairway Driver (Picture courtesy of Chris)

Van Aaken EGR valve control (Picture courtesy of Chris)

Connections into engine coolant system (Picture courtesy of Chris)

Van Aaken smartbox (Picture courtesy of Chris)

Diesel ECU smartbox


The TaxiCat System has no electronic controls or moving parts.

There are no complicated control modules, no drilling into engine components, and no connection into engine coolant system.

The system is supplied with a complete stainless steel exhaust.

The TaxiCat System is the simplest solution to enable cabs to meet the Euro 3 emissions regulations for London.

The benefits of that system are obvious in that there are no moving parts or electronics, and the exhaust purification is based on a "flow-though" catalyst rather than a filter or DPF. A complete stainless steel exhaust compliments the theme of durability and fit-and-forget.

A leading catalyst supplier developed a flow-through specifically for the taxi. It was important to resist the temptation of using a particulate filter, or "partial filter" as these devices can easily become problematic after a short period on vehicles that have inconsistent duty-cycles. Differential pressures and flow rates within the exhaust pipe and the engine air intake are used to provide varying amounts of exhaust gas recirculation. This simple approach reduces harmful emissions without the need for electronic controls and moving valves; both of which could be prone to failure. The exhaust to be returned to the the air intake is taken after the catalyst so that it is cleaner and rich in CO2.

A complete stainless exhaust was designed to give enhanced exhaust flow rates. This increases the efficiency of the engine by improving its ability to "breathe". Supplying a complete exhaust system also reduces the chances of miss-alignment and poor fitting of partial systems. The high quality stainless steel also eliminates future corrosion problems.

The TaxiCat System does not interfere with the engine coolant system therefore there are no increased risks of overheating. There is no drilling of any part of the vehicle or engine, and no need for electronic connections.
The TaxiCat System is approved for fitment to all LTI cabs fitted with Nissan engines.

TaxiCat System layout

TaxiCat System - Exhaust gas recirculation to air filter

TaxiCat System - flex-pipe from exhaust manifold to catalyst