The Anonymous Widower

Could London’s New Routemaster Buses Be Converted To Hydrogen Power?

There are a thousand New Routemaster buses on the roads of London.

This paragraph from  Wikipedia describes the transmission.

The bus is a hybrid diesel-electric driven by a battery-powered electric motor, charged by a diesel fuelled generator and recovering energy during braking by regenerative braking.


  1. The Cummins diesel engine is under the back stairs and is mounted high up. You can sometimes hear it start and stop if you sit or stand at the back of the bus.
  2. The diesel engine is part of the Cummins B Series Engine family, which is used very widely, included in vehicles like the Dodge Ram pick-up.
  3. The battery is mounted under the front stairs.

Cummins are embracing hydrogen in a big way and bought hydrogen company; Hydrogenics in 2019.

This press release from Cummins is entitled Cummins Begins Testing Of Hydrogen Fueled Internal Combustion Engine.

This is the first paragraph.

Cummins has taken another step forward in advancing zero carbon technology as the company began testing a hydrogen-fueled internal combustion engine. The proof-of-concept test is building on Cummins’ existing technology leadership in gaseous-fuel applications and powertrain leadership to create new power solutions that help customers meet the energy and environmental needs of the future.

Only today in Deutz Hydrogen Engine Ready For Market, I reported on how Deutz were going down a similar route.

I have done consultancy work for Cummins in Darlington, where I suspect the New Routemaster engines were built and the company prides itself in being able to provide a specially-laid out diesel engine for a niche-market application.

If they develop a hydrogen replacement for the B Series engine, I suspect that they will adopt the same sales philosophy.

For a start, it would enable all their many existing customers to convert their products from diesel to hydrogen power.

A hydrogen engine would be a direct way to enable conversion of a New Routemaster to hydrogen.

  • The new hydrogen engine and generator would just replace the current diesel engine and generator.
  • The chassis, body, battery and traction motor could be retained.
  • I am also sure, that Wrightbus have the expertise to squeeze a hydrogen tank in somewhere.

.I believe that in a few years Cummins will be able to replace the diesel engine with a hydrogen engine of equivalent size and power.

After Ricardo announced their fuel cell approach to convert modern diesel buses to hydrogen, which I wrote about in Ricardo To Engineer Zero Emission Buses For UK’s First Hydrogen Transport Hub, I am sure we’re going to see thousands of modern buses converted to hydrogen power.


I believe from my knowledge of Cummins and the way they work, that they will come up with a hydrogen-based solution, that will replace the Cummins diesel in these buses with a zero-carbon engine.

If Cummins don’t then someone else will.

Whoever solves the problem of converting London’s new Routemasters to hydrogen will have one of the best adverts for their product, there has ever been.

After converting London’s thousand Routemasters, the engineers could move on to anything powered by a Cummins engine.


August 18, 2021 - Posted by | Hydrogen, Transport/Travel | , , , , ,


  1. Well Borisbuses do have a 3rd entrance and 2nd staircase at the rear so removing these could provide more space for hydrogen power equipment and aid fare evasion and passengers safety .

    Comment by Melvyn | August 18, 2021 | Reply

    • Look at the cutaway drawings of the hydrogen bus here.

      I’m sure Wrightbus would have a cunning plan to get it right.

      Comment by AnonW | August 18, 2021 | Reply

    • The third entrance has been sealed up. They must be the worst buses I have ever been on. The lower deck is full of doors and stairs, the upper deck has a low ceiling, having to dick, with small seats. The colour scheme is depressing. The bus is poorly made with welds seen on what look like after-thought cross braces.

      They costed 2.5 time that of a normal bus.

      Comment by John | August 19, 2021 | Reply

  2. By 2025/26 manufacturers should be able to get CO2 emissions down to exceptionally low levels using hydrogen but that’s the first step. By 2030 or so Cummins, and all the other diesel engine manufacturers will be able to replace the engine with a hydrogen fuelled version not only of equivalent size and power, but also has an enhanced Brake Thermal Efficiency and will have optimised the combustion process. This is all explained by the leading combustion consultants, e.g. AVL, SWRI, Ricardo and FEW.
    Thermal efficiency of fuel cells should be better though.

    Comment by fammorris | August 18, 2021 | Reply

    • Replacing a diesel engine with a compatible hydrogen engine would mean that equipment makers could easily go zero-carbon without changing the transmission. Think of something like a farm tractor.

      Comment by AnonW | August 18, 2021 | Reply

      • I don’t know what you mean by referring to farm tractors but your first sentence confirms what I was thinking about.

        Comment by fammorris | August 18, 2021

  3. In it’s simplest form, a farm tractor is just an engine driving the two rear wheels, with attachments like power take offs on the transmission.

    If you could replace the diesel with a hydrogen engine, all the gubbins won’t need to be redesigned.

    Comment by AnonW | August 19, 2021 | Reply

    • Yes, but I just didn’t understand the uniqueness of a farm tractor, a traditional truck or automobile driveline would have served your observation equally well 🙂

      Comment by fammorris | August 19, 2021 | Reply

  4. Using hydrogen in piston internal combustion engines is a dumb idea. They are still noisy, vibrate, etc. They are still only 20% efficient as teh engine is such a poor design, with so many pumping losses.

    The Wankel engine, one third if the size and weight of an equivalent piston engine, which is far smoother, increases efficiency by 27% when using hydrogen. Using a Hydrogen Wankel is better than a piston engine all around. The efficiency rises when run at constant speeds, such hybrid genny applications.

    Comment by John | August 19, 2021 | Reply

  5. If Hydrogen and Oxygen are burnt, the emissions will be zero. Air contains about 78% Nitrogen – if Hydrogen and air is burnt, NOx will be produced, which is a nasty pollutant. So H2 burning is zero carbon dioxide, but NOT zero emissions. So do not get sucked into the 100% clean hydrogen myth.

    There is talk of converting the natural gas pipe network into buildings to hydrogen. A part of the UK is already 5% hydrogen, 95% natural gas mix – Gateshead. 20% of the mix can be hydrogen with all existing appliances able to burn without problems. This drops emissions substantially. 30% of all the UK emissions are via natural gas. New appliances have to be hydrogen ready with only adjustments on conversion. Old appliances maybe a new burner.

    I would never have a hydrogen gas cooker or gas fire, only a room sealed boiler.

    Flats cannot have gas in them, with all new builds all electric.

    Comment by John | August 19, 2021 | Reply

  6. Your last point is the most important.

    I lived in a 1960s built flat which was all electric. No naked flames meant my health was better.

    But if all those 1960s built flats like Grenfell had been built without gas, how many lives would have been saved.

    As an aside, I backed the development of a metered dose inhaler for asthma drugs and learned a lot about asthma.

    It convinced me never to have any naked flames from gas, matches, fags or bonfires anywhere near myself.

    Comment by AnonW | August 19, 2021 | Reply

  7. Interesting to understand where you’re getting your references from for such assertions for ICEs and the Wankel engine.

    Comment by fammorris | August 19, 2021 | Reply

    • I know nothing about Wankels. With ICEs companies have so much invested in the technology and various companies have shown it can be repurposed.

      Comment by AnonW | August 19, 2021 | Reply

      • Sorry that was a question for John

        Comment by fammorris | August 19, 2021

      • Piston ICE engines are very crude and very inefficient.

        Comment by John | August 20, 2021

    • Development of Hydrogen Rotary Engine Vehicles…

      Click to access 169.pdf

      The Wankel engine has known problems in fuel efficiency and emissions when burning petrol. Petrol mixtures are slow to ignite, have a slow flame propagation speed and a higher quenching distance on the compression cycle of 2 mm compared to hydrogen’s 0.6 mm. Fuel is wasted that would have created power, reducing efficiency. The gap between the rotor and the engine housing is too narrow for a petrol/air mix on the compression cycle, but wide enough for hydrogen. When the Wankel engine uses petrol, leftover unburnt petrol is ejected into the atmosphere. This is not a problem when burning hydrogen, as all the fuel mixture in the combustion chamber is burnt which gives vastly reduced emissions, raising fuel efficiency by 23%.

      But that is a 23% increase on an already low base. I know of no other way to increase piston engine efficiency by 23% at a stroke. Mazda did sell a hydrogen Wankel engine car – only in Japan. I recall it was switchable from hydrogen to petrol, the Mazda RX-8 Hydrogen RE.

      Wankel engines can better piston engines if run at constant speeds – like genny applications. They do not like being revved up and down. They are ideal for hybrids. Mazda announced the Wankle hybrid MX-30 (made and working) – it keeps being delayed. It seems too little too late as EV are to take over.

      Comment by John | August 20, 2021 | Reply

      • Good vid by Jason:

        Incrase of 28%

        Comment by John | August 20, 2021

      • Thanks for the background informati

        Comment by fammorris | August 20, 2021

  8. There’s also this free piston engine from Aquarius.

    New Hydrogen Engine Design Unveiled To Overcome Reliance On Fuel Cells

    Comment by AnonW | August 20, 2021 | Reply

    • Free piston engines have been in R&D for many years but no one has made one commercially viable yet.

      Comment by John | August 20, 2021 | Reply

  9. […] I wrote about converting London’s New Routemasters to hydrogen in Could London’s New Routemaster Buses Be Converted To Hydrogen Power?. […]

    Pingback by Repowering Zero-Emission Buses As An Alternative « The Anonymous Widower | July 24, 2022 | Reply

  10. Why do you need to replace the generator?

    How about connecting the hydrogen engine to the existing generator?

    Comment by chilterntrev | July 24, 2022 | Reply

  11. I wouldn’t be surprised to see Cummins produce a reciprocating hydrogen engine, that had the same dimensions as the engine in the Routemaster. There are hundreds of thousands, if not millions of these B series engines in use around the world. So reengining could be a lot bigger than a thousand London buses.

    Comment by AnonW | July 24, 2022 | Reply

    • According to a Cummins press release in May they do not anticipate having mass produced engines capable of running with hydrogen until 2027, and then only with 15 and 6.7 litre units, so I guess we’ll have to wait a bit longer for a direct replacement.

      Comment by fammorris | July 24, 2022 | Reply

      • Someone will do something! After all, if Clean Air Power of Melton Mowbray can get a Class 66 locomotive to run on hydrogen, someone will rise to the challenge.

        Comment by AnonW | July 24, 2022

  12. AnonW, according to recent press release Clean Air Power demonstrated a Freightliner Class 66 locomotive, allowing the two-stroke diesel locomotive to run on a combination of diesel, biogas and hydrogen. We don’t have the proportions of how those fuels were mixed. The reduction in methane emissions is impressive but until we know more about the fuel mixture it will be hard to believe that running what is currently a compression ignition engine on hydrogen, without significant further modification to address NOx emissions and the engine’s lubrication, is a viable option in the next few years.

    Comment by fammorris | July 25, 2022 | Reply

  13. […] A classic application would be converting London’s Routemaster buses to hydrogen, which I wrote about in Could London’s New Routemaster Buses Be Converted To Hydrogen Power? […]

    Pingback by The Third Route To Zero-Carbon Transport « The Anonymous Widower | August 23, 2022 | Reply

  14. […] Could London’s New Routemaster Buses Be Converted To Hydrogen Power?, I came to this […]

    Pingback by My First Ride In A Refurbished New Routemaster « The Anonymous Widower | September 20, 2022 | Reply

  15. […] Could London’s New Routemaster Buses Be Converted To Hydrogen Power? […]

    Pingback by Cummins And Accelera Showcase Broadest Portfolio Of Decarbonizing Technologies With An Emphasis On Hydrogen « The Anonymous Widower | May 3, 2023 | Reply

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