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About Us

HJS Emission Technology was founded in 1976 with its headquarters based in Menden, Central Germany. HJS employs approximately 450 people who are engaged in the development, production and marketing of modular exhaust systems for reducing emissions for all road, rail, construction and marine applications.


Our business in the UK is supported by our dedicated sales, project management and technical teams operating from our facility in Swindon, Wiltshire.  From this facility, our engineering team provide nationwide installation and technical support.

The reduction of Nitrogen Oxides (NOx) contributing to air pollution is one of the most challenging public health issues facing the UK today.  Diesel exhaust emissions have been classified as carcinogenic to humans, reassigning it to the same class of hazardous materials as asbestos, arsenic and mustard gas.  The majority of urban areas in the UK are struggling to meet stringent European requirements for NOx emissions and the government has been ordered by the Supreme Court to take action in the quickest time possible.

HJS work together with bus/coach operators and local authorities to improve air quality across the country.  HJS are the pioneers of Selective Catalytic Reduction Technology (SCRT®) which can be retrofitted to significantly reduce NOx emissions and also virtually eliminate particulate matter.  The HJS Real Blue SCRT® system meets Euro VI standards and is both ULEZ and CAZ compliant. System performance has been certified at Millbrook Proving Ground which has been followed up by several months of successful in service testing.

In 2019, Transport for London will introduce a 24/7 Ultra Low Emission Zone (ULEZ) to improve the problem of urban air quality in the capital.  In addition to this Birmingham, Nottingham, Derby, Southampton and Leeds will be introducing Clean Air Zones (CAZ’s). 28 more cities and towns have also been identified requiring additional measures and Glasgow will become Scotland’s first Low Emission Zone at the end of 2018.

The HJS Real Blue SCRT® system is accredited by the Energy Saving Trust’s CVRAS (Clean Vehicle Reduction Technology Scheme). Our approved technology allows vehicles to be upgraded to meet LEZ, ULEZ and CAZ requirements and complies with the conditions set out within the Clean Bus Technology Fund (CBTF).



For over 40 years, HJS has established itself as an innovative company with national and international benchmarks for the automotive industry.Continue reading »


HJS has been developing technologies for environmentally friendly mobility as the basis for a clean future since the 1980s.Continue reading »


Our project and infrastructure enables flexible and individual implementation of projects at attractive costs.Continue reading »


We owe our business success not only to the high quality of our products and processes, but also to their continuous improvement.Continue reading »

Our Mission zero emissions

Business areas

Bus & Coach – Euro 6 retrofit upgrades

The SCRT® system combines a diesel particulate filter with an SCR unit for the reduction of nitrogen oxides. New buses that are already fitted with particulate filters can be retrofitted with an SCR unit to create an SCRT® system. Likewise, older vehicles without an exhaust treatment system can be retrofitted with an SCRT® system. SCRT® is currently the most advanced and effective exhaust gas aftertreatment technology available.

With the aid of an HJS filter soot particles can be filtered from diesel exhaust gases down to the limit of detection. It’s not just particulate matter that pollutes the environment and damages people’s health: gaseous substances such as Nitrogen Oxides are also harmful. In order to reduce the levels of these gases, HJS has contributed to the development of the SCRT® (Selective Catalytic Reduction Technology) system over the last 25 years.



  • Direct fit systems with full vehicle integration
  • Reduced installation time
  • Decreased engine noise level
  • Urea pump exchange optional
  • Communication via CAN
  • HJS diagnostic software package
  • OEM diagnostics not influenced
  • OEM sensors can be retained
  • Fully integrated telematics for system monitoring
  • Low maintenance intervals
  • OE quality systems made in Germany

Retrofit to EURO 6 emission standards

The cost effective conversion for ULEZ and CAZ compliance

  • Bus and coach operators can upgrade to EURO VI diesel emission standards

  • Millbrook certified solutions for the ULEZ in London and UK Clean Air Zones

  • A range of applications available for the most common buses in the UK

  • Over 3,000 transport vehicles throughout Europe are installed with the HJS SCRT®

  • Designed and manufactured in Germany to Original Equipment standards

  • Vehicle Certification Agency (VCA) approved

  • Clean Vehicle Retrofit Accreditation Scheme (CVRAS) approved

Lowest NOx emissions in real operation

  • Retrofitting of EURO III, IV, V and EEV city buses to EURO VI
  • Efficiency
    • Over 99% reduction of soot particles, including fine particles
    • Up to 99% reduction of nitrogen oxides (NOx / NO2)
    • Over 95% reduction of gaseous pollutants (CO / HC)
  • Low maintenance and cost effective
  • Live system performance monitoring via the HJS telematics system

HJS Telematics Module – Aftertreatment Connectivity 4.0

System operating information is logged at a frequency of 1Hz to 1,000Hz by the HJS telematics unit. All recorded data is then stored as a file which is then uploaded to the Cloud system every 2 to 10 minutes ensuring that the most recent data is available to view. If the GSM connection is temporarily unavailable, the telematics system will buffer the data until the data network connection is restored and data re-transmission will occur.

Where predetermined system operating limits are breached or if system servicing is required, text message and email alerts can be created.

Current SCRT® application range

  • ADL Enviro 200 EURO IV/V

  • ADL Enviro 400H EURO V

  • ADL Enviro 400 Euro IV/V

  • DAF BD250

  • Volvo B5LH EURO V

  • Dennis Dart – Cummins ISBe 4

  • Dennis Trident – Cummins ISBe 6

  • EvoBus Citaro G – 457 hLA

  • EvoBus Citaro S – 906 hLA / 906 LA

  • IVECO City class Cursor

  • MAN A 23 (D2866)

  • SCANIA Omnicity


  • VDL Ambassador SB 200 – ISBe 22030

  • Volvo 8700 BLE – DH12D340

  • Volvo B7TL

HJS Emission Technology at glance

  • Founded in 1976 by Hermann Josef Schulte

  • Headquarters in Menden, central Germany

  • Number of employees 400

  • Family owned business

  • Wide range of proven retrofit emission control products

  • R&D engineering competences for diesel and petrol engines

  • OE series experience [VW, Daimler, MAN, etc.]

  • Flexible manufacturing structures

Taxis – Euro 6 conversion

  • Taxis are a significant contributor to London’s toxic air quality, and are responsible for 16% of NOx and 26% of Particulate Matter (PM) emissions in central London.
  • HJS offers a cost effective solution to reach Euro 6 standards by retrofitting a highly efficient SCR system.
  • The vehicles will be approved according to the Energy Savings Trusts Clean Vehicle Retrofit Accreditation Scheme (CVRAS).


System design

System diagram

Taxi Concept – Euro 6 Taxi conversion

Retrofit system completely independent no impact on engine control unit


Convert your Taxi from Euro 5 to Euro 6 Emission Standards with HJS Retrofit SCR Technology

  • HJS Emission Technology have developed a range of retrofit Selective Catalytic Reduction (SCR) exhaust systems that enable drivers of Euro 5 diesel taxis to upgrade to Euro 6 emission standards.
  • HJS retrofit conversions are currently available for the Euro 5 LTi TX4, the Mercedes Vito and Peugeot E7 taxis.  All systems have been tested and approved by the Clean Vehicle Retrofit Accreditation Scheme (CVRAS) which is managed by the Energy Saving Trust.
  • HJS Selective Catalytic Reduction (SCR) is an advanced active emissions control system that can reduce exhaust tailpipe emissions of nitrogen oxides (NOx) by over 90%.
  • The HJS SCR system operates in conjunction with the vehicles existing DPF which already meets the requirements for the reduction of Particulate Matter. The SCR system supplied by HJS consists of an underfloor catalyst, an Adblue tank with airless pump, a variety of sensors and an independent control unit with driver information display.
  • The SCR system operates by injecting Adblue (an Ammonia based solution) directly into the exhaust gas stream. The Adblue is mixed with the dirty exhaust gases and passes over the SCR catalyst converting Nitrogen Dioxide emissions into mainly water and Nitrogen.
  • SCR retrofit systems have already helped many drivers across the UK to comply with Local Authority Clean Air Zone requirements and avoid the daily access charges.  In many cases, government grant funding has been made available to support the taxi trade to upgrade their vehicles.
  • Retrofitting existing taxis to meet Euro 6 emission standards is a highly cost-effective way for drivers to avoid the daily access charges and can also give the vehicle a longer life span and can increase its value.  It will also help drivers to reduce their environmental impact and contribute to local air quality improvements.
  • The SCR system is manufactured in Germany to the highest standard and can normally be installed within one day.

Taxi SCR-system

Sensor and dosing valve usage and position

Diagnosis concept

Installation of 2 lamps in the dashboard for MIL (yellow) and refilling AdBlue (blue)


  • Electrical diagnosis of all actuators and sensors
  • Further diagnosis functions (depending on system scope)
  • plausibility check of sensor signals,
  • plausibility check of NOx conversion (NOx sensor ds SCR required)
  • AdBlue level
    request for refilling AdBlue when level below certain limit (lamp)
    MIL activation when level drops below minimum threshold, error message to ECU
    possible if requested
  • AdBlue quality
    MIL activation if quality is out of range, error message to ECU possible if requested
  • No derating measures by ACU

Rolling Stock

Innovative emission reduction technologies
for the rail industry

HJS have contributed to air quality improvements in the rail sector for
several years providing emission reduction exhaust systems equipped
with its innovative Sintered Metal Filter (SMF®) technology for
PM reduction.
Due to its unique design, the HJS SMF® has significant advantages in
comparison to conventional honeycomb filters in terms of ash loading
capacity and cleanability resulting in significantly lower ownership
costs over its life time. The ash loading capacity of an SMF® is approximately
1.8 times higher than a conventional filter which leads to up
to 30% more operating hours between cleaning cycles.
The SMF® has an open pocket structure allowing access to any ash
stored which can then be cleaned using a conventional pressure
washer. In summary, the HJS SMF® offers some key advantages when
compared to conventional DPF systems.

HJS UK emission reduction rail projects

HJS UK have teamed up with Vivarail to provide particulate reduction
systems for their innovative diesel hybrid powered solution being installed
onto ex London underground rolling stock. Vivarail trains are
now being used on several commuter branch lines to boost passenger
capacity whilst reducing environmental impact thanks to the HJS SMF®.
With numerous inner city low emission zones and clean air zones being
introduced, the pressure is increasing on rail operators to reduce their
impact on air quality. In order to develop its NOx reduction applications
for the rail industry further, HJS UK are working closely with one of
the largest train leasing companies in the UK. The HJS SMF® will be
used in conjunction with an HJS SCR system to provide a substantial
reduction of PM, NOx and NO2 on a Cummins powered DMU.

HJS has been an OE supplier of exhaust-gas treatment systems to rail construction
manufacturers such as Plasser & Teurer and Robel (together with
various other companies) for over 10 years.

The higher ash storage capacity results in higher possible mileages
betweencleaning cycles within a range of 25 – 30 %.

Millbrook testing was a great success and fitment to an operating DMU is expected imminently

Commercial vehicles / LCV Euro 6 retrofits

To improve air quality across the UK diesel van and mini bus owners can upgrade their vehicle using the HJS Euro 6 retrofit conversion.  Our ULEZ retrofit and Clean Air Zone retrofit (CAZ retrofit) offer compliance to enter these zones charge free.  HJS are the first company to offer Euro 6 conversions for vans and Euro 6 conversions for taxi’s.

Visit Low Duty Vehicles


Go to “Cybrand”

Installation Partners


London Taxi distributor

NRMM / Genset Emission Reduction Retrofits

HJS are the first retrofit exhaust system manufacturer to secure Energy Saving Trust (EST) certification for all power bands of fixed and variable speed Non Road Mobile Machinery (NRMM) applications. This includes approval for Stage 3b and Stage 4  engines where a compliant OE DPF is already fitted, and an HJS SCR system is retrofitted to achieve Stage 5.

HJS have worked tirelessly over the last 2 years with the Swiss Association VERT and have undertaken strict in-service testing in order to gain this accreditation.

In the current climate of uncertainty where compliant machinery is not widely available, the HJS SCR/T system gives NRMM owners and operators a cost-effective and timely alternative to purchasing new Stage 5 machinery.

Contact us today to discuss retrofitting your existing equipment to gain Stage 5 compliance. This is essential for the Greater London Authority NRMM low emission zone, on key infrastructure projects such as HS2, and on a growing number of key construction sites across the UK.

The Greater London Authority Low Emission Zone for Non Road Mobile Machinery  

The Low Emission Zone in London applies to all Non Road Mobile Machinery (NRMM) with a net power rating of between 37kw and 560kw operating within central London.

The minimum emission standards for NRMM within London are detailed below:

  • NRMM used on the site of any major development, as defined in the London Plan within Greater London will be required to meet emission Stage 3A as a minimum

  • NRMM used on any site within the Central Activity Zone or Canary Wharf will be required to meet emission Stage 3B as a minimum

  • All eligible NRMM should meet the standards above unless it can be demonstrated that a comprehensive retrofit to meet both PM and NOx emission standards is not feasible. In this situation every effort should be made to use the least polluting equipment available including retrofitting technologies to reduce particulate matter emissions

Central Activity Zone or Canary Wharf Greater London
From Sept 2020 Stage IV or best available retrofit technology Stage IIIB or best available retrofit technology 

With an estimated 10,000 active construction sites in London at any one time NRMM has been identified as one of the largest contributors to poor air quality in London.

Plant hire companies machine operators and construction organisations have the following compliance options:-

  • Retrofit existing machines with emission abatement technologies

  • Reorganise NRMM fleet to ensure compliant equipment is used

  • Replace or re-engine equipment

For the majority of operators the retrofitting of existing machinery will be the quickest, most effective and most reliable way of ensuring that they comply with the conditions set within the LEZ.

To find out more visit the energy savings trust website :- Click Here


HJS have installed thousands of emission abatement systems throughout the UK and Europe.  These systems require regular servicing and maintenance in order to ensure efficient operation and maximum reliability.  HJS’s dedicated team of specialist technicians can offer the full service and maintenance packages and more.  Packages can be tailored to suit the requirements of our customers.

Our engineers are also able to troubleshoot and help diagnose vehicle issues which are reducing system servicing intervals.

To discuss your servicing options give us a call today on 01344 566050

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HJS Emission Technology Ltd

Unit 11
Rushy Platt
Industrial Estate
Caen View
Swindon SN5 8WQ
United Kingdom


Mark Cooper
Head of Business Development and Sales
07733 227 889

All sales enquiries call : 01344 566050

All aftersales and service enquiries call:

Dave Andrews
Operations Manager
Mobile: +49 160 93467187

Ben Parsons
Technical Project Manager/Service Manager
07716 639650

Lamar Stevens
Technical Aftersales Manager
07885 489547

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