About Us

HJS Emission Technology was founded in 1976 with its headquarters based in Menden, Central Germany.   HJS employs approximately 400 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 Bracknell, Berkshire.  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


Bus & Coach

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 VI emission standards

The cost effective solution 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 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

  • Retrofit system completely independentà no impact on engine control unit
  • Existing exhaust aftertreatment components DOC and DPF remain
  • Standard OE parts used as retrofit components (dosing system, AdBlue tank, sensors)
  • Usage of serial OE SCR coatings
  • HJS ACU as control unit, already used in several OE systems
  • AdBlue dosing strategy is based on sensor signals (temperature, NOx) directly measured in exhaust flow and additional data from engine CAN (exhaust mass)
  • Modular system design
    • Additional components available to operate under low temperature profiles
    • Heating element (thermal management)

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

Commercial vehicles

To help improve air quality across UK diesel vans and mini busses will need to meet new tighter emission standards called the Clean Air Zone Standards or Ultra Low Emission Zone (ULEZ) standards in several UK countries.

Visit Low Duty Vehicles

Installation Partners

Go to “Alliance”

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

Contact Us

Emission Engineering Ltd

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


Mark Cooper
Managing Director
07733 227 889

Ben Parsons
Technical Project Manager
07716 639650

Gerd van Aaken
07949 123 361


Our partner:

Cybrand AEC Ltd
Phone 01244 567100

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