Air QualityEnvironment & ClimateHeavy Duty & Off-highwayHydrogenSustainabilityThermoPower

World Health Day, 7th April 2022. How some cities are combatting air pollution & focussing on human health & wellbeing.

By April 7, 2022 No Comments

With an estimated 55% of the world’s population – 4.2 billion inhabitants living in cities there is an ever-growing need for cities to clean up their air, with polluted air quality being cited as a contributor to premature deaths globally.

2016 figures showed that 90% of urban dwellers had been breathing unsafe air with more than half of the global urban population being exposed to air pollution levels at least 2.5 times higher than the safety standard. (1)

During the first waves of the Covid19 lockdowns, across the globe CO2 emissions dropped dramatically (albeit only a temporarily while strict restrictions were in place) & this was all due to the lack of human movement. With & equally how much they have sadly bounced back & in some areas superseded pre-Covid levels.

With the ever-growing need for cites to clean up their air, many cities are moving to electrification, ULEZ’s & in some cases, banning cars & combustion engine vehicles all together.

These initiatives may be  a vital component for the health of the human inhabitants of said cities & for the wider global impact but it gives rise to a question; how do commercial companies deliver life necessities to inner cities without the use of haulage, trains or in some cases, shipping channels? & furthermore, how does the building trade manage to receive the vast building materials, without the delivery power of a combustion engine vehicle?

The Dolphin N2 ThermoPower (TM) Recuperated Split Cycle Engine is one solution to the need for heavy duty vehicles to still be on the road, but be functioning at zero emissions. Nick Owen – Technical Director, Dolphin N2 recently presented as part of a seminar at the Future Propulsion Conference & explained in more detail why the Dolphin N2 ThermoPower (TM) system is applicable in an inner city context.

Dolphin N2 ThermoPower (TM) Recuperated Split Cycle Engine

The Dolphin N2 technology specifically targets heavy duty & the long-haul sectors where most commercial vehicle CO2 originates & alternatives are the most challenging.

The Basic Cycle of the Recuperated Spilt Cycle Engine is made up of: Dedicated Cold & Hot cylinders of unequal size, Insulation of hot cylinder, Recuperation of exhaust energy, Low-NOx Cool Combustion enabled by dense sonic intake air & Cooled Compression.

Dolphin N2 have had a multi-cylinder prototype of the running engine since December 2020 & the data already looks promising with high thermal efficiency –55-60% BTE, low emissions – NOx at SULEV or below with standard SCR & fuel compatibility with Diesel, Methane & Hydrogen

Although the Dolphin N2 engine & the technology built around it uses the efficiency of a diesel engine as it’s base model, the developments mean that the RSCE can also be run on methane & hydrogen.

Hydrogen is politically favoured as an “alternative to electricity” for an on-highway application as it is already readily produced from renewables, with zero “source to tank” & net GHG (which matters) Hydrogen also produces zero GHG at the tailpipe (politically popular), is fairly quick to refuel – the energy density is acceptable with compromise & it suits both Fuel Cell & ICE – creating critical mass of demand.

The benefits of a Hydrogen ICE are that a Hydrogen ICE works, is fast to adopt, uses the same supply chain as current manufacturers, has familiar servicing needs, NOx is entirely manageable via lean burn & in principle it suits a Recuperated Split Cycle. “Fast oxidation” combustion is fuel agnostic – violent mixing with red-hot sonic & supercritical air will burn many things & if Hydrogen can maintain BOTH high efficiency & low NOx, the advantages are clear.

Car free cities & ULEZ

Many international cities have already been taking bold steps to reduce CO2 emissions & particulate matter in inner city settings. Oslo banned cars from the city in 2019, Copenhagen – home to the largest car free zone in Europe – began removing cars from the city centre in the 1960’s & Madrid slowly removed all cars, except for residents’ vehicles during 2019.

In the UK, the ULEZ (Ultra Low Emission Zone) has, under Mayor Sadiq Khan’s leadership, been extended further & further to remove polluting vehicles from the centre of London. With this in mind, the City of London’s Environment Strategy intends to integrate:

  • air quality
  • green infrastructure
  • climate change mitigation and energy
  • waste
  • adapting to climate change
  • ambient noise
  • low carbon circular economy (2)

With a clear message that the Mayor wants all diesel vehicles & those who do not adhere to the ULEZ expectations to be banned form the City by 2037, with buses, taxes & other infrastructure vehicles being either electric, hydrogen or low emissions capable; Sadiq Khan’s mission for a cleaner London is expanding fast.

London is not the only city looking to expand the clean air spaces & reduce & or ban cars in the city.

More ULEZ’s have been introduced across the UK, with Glasgow, Bath, Birmingham, Manchester & Portsmouth already introducing low emission zones in an attempt to combat inner city pollution. Further afield, Paris & Barcelona are also making changes to their cityscapes.


In 2020 Mayor Hidalgo announced grand changes to the Champs-Élysées avenue.  Since 2018, the Champs-Élysées committee has been developing plans for a garden to be built on the 2 km promenade between the Arc de Triomphe & Concorde.

Despite the fact that the French call it “the most beautiful avenue in the world”, the grand avenue now resembles more of a highway, with tens of thousands of cars passing by each day. (3)

The planned garden is set to reduce traffic by up to 72% & in doing so dramatically reduce the CO2 emissions in the Capital.


The City of Barcelona is currently battling with excessive noise & air pollution. The idea of integrating what is known as superblocks – mini neighbourhoods around which traffic will flow, and in which spaces will be repurposed.

The proposed idea formulated by BCNecologia, an agency led by Salvador Rueda, Director of Urban Ecology Agency of Barcelona; claims that the extension of the current superblock scheme would reduce ambient levels of NO2 by 24%, from the current level of 47 micrograms per cubic metre to 36 micrograms per cubic metre. (4)

A decrease on that scale would bring Barcelona’s NO2 levels into line with the WHO recommendation of a maximum of 40 micrograms per cubic metre. (4)

Superblocks will be complemented by the introduction of 300km of new cycling lanes (there are currently around 100km), as well as an orthogonal bus network that has already been put in place, whereby buses only navigate a series of main thoroughfares. (4)

One of the other important changes in inner cities is the development of green spaces. The need to offset the affects of climate change are evident in such projects as rewilding & afforestation. With cityscapes not necessarily allowing these projects, many have taken to rooftops to increase green spaces & in doing so, help to improve air quality.

As part of the Urban Greening strategy set out by the Mayor of London, the greening of London’s streets, buildings & other public spaces, does more than change the look of these places. Roofs & walls covered in plants, street trees & small pocket parks in between buildings make the city a better place to live, work & invest. These green features act as part of London’s green infrastructure network to help clean the air, reduce the risk of flooding & keep the city cool. (5)

With an ever growing need to offset the pollutants in inner cities & mitigate their affect on human health; cities around the world are focussing more & more on reducing tailpipe emissions from cars/trucks & introducing green spaces/vertical & rooftop gardens to try & combat the effects of climate change on their inhabitants.

Written & cited by Katy-Jane Mason for & on behalf of Dolphin N2.