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First liquid nitrogen hybrid bus completes trials; HORIBA MIRA and Dearman

A hybrid bus that runs on both diesel and liquid nitrogen has completed a series of trials to bring it one step closer to the road. The hybrid bus—CE Power—is the first to be powered by liquid nitrogen and has been built by engineers at HORIBA MIRA as part of an Innovate UK consortium.

The bus utilizes alternative propulsion to address urban air pollution challenges and features a high-efficiency, zero-emission Dearman Engine (earlier post), powered by liquid nitrogen, alongside a conventional diesel engine. The hybrid system enables the bus to reduce noxious tail-pipe emissions, improving local air quality.


The Innovate UK consortium comprised industry, academic and local and national governmental organisations. It was led by Dearman and included Air Products, Cenex, Coventry University, HORIBA MIRA, Manufacturing Technology Centre, Productiv Ltd, and TRL (the Transport Research Laboratory).

The bus uses a hybrid propulsion system to reduce emissions during acceleration after stopping. This portion of the bus’ drive cycle traditionally has a heavy impact on the diesel engine and can produce large amounts of NOx and CO2 emissions. As the Dearman Engine produces none of these harmful emissions, it will enable the bus to continue to stop frequently to unload and pull away from a bus stop without expelling the same level of damaging pollutants.

While driving at 20 mph or below, the liquid nitrogen—stored in a low pressure insulated cylinder—s warmed up to the point of boiling, at which time it creates enough pressure to drive the multi-cylinder Dearman engine. Once the bus reaches 20 mph, the diesel engine will kick in as at this speed the bus requires less effort from the engine to operate.

The development of an on-vehicle cryogenic system was a notable achievement to come from the project. The innovative system was developed by the consortium team to store cryogenic nitrogen liquid at low pressure, then pressurize and store in high pressure cylinders for use in the Dearman engine. This stored pressure is then used to provide the rapid reaction pressure responses required.

—Jon Trembley, Head of Cryogenic Technology at Air Products

The bus trials were completed at HORIBA MIRA’s engineering facilities and Proving Ground in Nuneaton and included components and full system testing along with an engineered drive cycle to simulate a standard bus route with a variety of stops.

The Dearman Engine has the potential to significantly improve the efficiency of both buses and HGVs, reducing fuel consumption and cutting pollution. Crucially it can provide a cost effective alternative to other emerging zero emission technologies, whose environmental performance if often offset by complexity and cost. This successful trial could be the first step towards rolling out a British innovation to the streets of the UK and around the world.

—David Sanders, Commercial Director at Dearman

The benefits of using liquid nitrogen over an electric hybrid bus include a much longer life, local production and easy refueling. Batteries, which power many of the UK’s electric hybrids, require changing several times over the course of a bus’s lifetime, whereas the liquid nitrogen system will last the lifetime of the bus, Dearman said. Liquid nitrogen can be produced locally without the need for neodymium or lithium, which are both used by motors and batteries and sourced from overseas. Furthermore, refueling liquid nitrogen can take a matter of minutes, enabling the bus to return to the road in a short timeframe.

The hybrid nature of CE Power demanded a sleek systems integration process. Our engineers worked to ensure the liquid nitrogen system operates seamlessly and safely with the diesel engine, in addition to carrying out the whole vehicle thermodynamics modelling and the overall vehicle control and testing. The completion of these trials paves the way for the use of liquid nitrogen more widely in the automotive sector, and takes the UK one step closer to stamping out harmful emissions for good.

—Martin Watkinson, Technical Lead on the project at HORIBA MIRA



Sounds good, I am all for hybridisation as long as it is affordable - and the more techniques, the merrier.

It sounds more like a PHEV (or a FHEV) [Fuel, HEV] - can it do regenerative braking, or do they just use the n2 for acceleration ?


"Highview Power’s process is 50 to 60 percent efficient—the liquid air can yield just over half as much electricity as it takes to make it."


Brent Jatko

I am wondering about the energy balance. Is more energy required to compress and cool the liquid nitrogen than is saved by assisting the diesel up to 20 mph?

Or is this a tool to reduce urban diesel emissions (a worthwhile goal, IMO)?

Account Deleted

Someone needs to combine the Dearman Engine (a Liquid Air Heat Recovery engine), the the Highview Power Liquid Air Energy Storage System, with the NetPower Supercritical CO2 Gas Turbine using the Allam Cycle.
The NetPower Supercritical CO2 Gas Turbine (which can reuse or capture all of the CO2 and has 59% LHV efficiency) only major expense addition is an Air Separation Unit which must separate the Oxygen from the air to feed the Gas Turbine to create a pure CO2 stream.
If this Air Separation unit was also used as an Energy Storage System some of that expense would allow the NetPower Turbine to be used as a Load Follower Powerplant instead of just a Base Load Powerplant (the NetPower Turbine would take at least 15 minutes to come online to backup Wind and Solar Generation).


The Dearman model seems unambitious, failing to take full advantage of the resources of the rest of the bus.  Take the engine exhaust.  It is quite hot, probably 3x the ambient absolute temperature at a minimum.  It would be a fairly simple matter to add a heat exchanger to heat pressurized N2 (after exploiting it for A/C purposes) to several hundred degrees C.  This would roughly triple the volume at the same pressure and triple the expansion work.  Heat could be stored for longer periods of engine-off operation by adding some salt tubes to a counter-current heat exchanger.

I notice that there's no comparison to a hydraulic hybrid, which could do the same emission-free launch but requires no cryogenic fluids whatsoever.


This is still an obsolete internal combustion engine burning carbon in the air. Nothing really new here except added complexity.


Lol, they explicitly admitted that batteries are costly and do not last a long time. I was right about it since a long time and that lie was told and spreaded by the inter-planetary climate scientist like leonardo di caprio, armold swarthzennegger algore, ipcc, volt, leaf, tesla, everyday, apple, google, ipcc, . I taught that the nissan serial hydrid is the way to go if they start to harness at my benefit exhaust heat and pressure from cheap gasoline.


No rare earth magnets nor lithium, separate, compress and chill nitrogen on site. It reduces particulates created during takeoff from a stop...I like it!


Apparently, diesel engine compression readings are on the order of 275 to 400 psig depending.

Why the diesel engine of the bus cannot be used to compress air into a tank, and the air used to drive the bus away from the stop until the tank is depleted and the engine must be started in combustion mode, is a mystery to me.  Someone wants the public to believe that liquid nitrogen is a sine qua non for such things.  Who is this someone?

Sam Bacca

It is very pleasant to see a new kind of hybrid bus that will run on the liquid nitrogen and diesel. You can hire an academic essay writer to get a well written essay. Projects like liquid nitrogen hydro bus would surely be very helpful in overcoming air population challenges.

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