A fleet decarbonisation strategy for the diesel fleet you run today

Replacing a fleet takes as long as its replacement cycle. Until then, the fuel burned by the diesel vehicles within your organisational boundary counts towards your Scope 1 emissions — so decarbonisation starts with those litres. A workable order: measure the baseline, burn fewer litres with measures that need little or no capital, switch fuel where it is available and makes sense, and replace vehicles when they are due. Where fleet emissions are calculated from fuel use, every litre of the same fuel not burned lowers the calculated figure — and, where a carbon price applies, the cost.

This guide is about trucks, buses, vans and municipal vehicles. Where an air-filter treatment such as NanoEFX fits is set out in its own section below, with what our trials show and what they do not.

For vehicles within a company’s organisational boundary, fuel combustion is a Scope 1 source under the Greenhouse Gas Protocol. A common way to quantify it is from activity data — the fuel burned or the distance driven, multiplied by default or own emission factors for carbon dioxide, methane and nitrous oxide — rather than measuring the exhaust directly (GHG Protocol — accessed 15 October 2026). Fuel records are therefore the practical basis this guide works with, and the levers are the litres themselves and the fuel in each litre.

The same litres carry the carbon cost. Where a carbon tax or emissions trading applies to road fuel, the price arrives per litre — our overview of carbon tax on diesel by country shows how much. New drive systems change the energy a vehicle uses, but only for the vehicles that are replaced, and only from the day they arrive.

Change one thing at a time, or keep comparable vehicles without the change. If driver training, new tyres and a treatment start in the same month, no one can say afterwards what saved what — and an unproven saving does not survive an audit or a budget review.

NanoEFX is applied to the engine’s existing air filter during routine servicing and re-applied at a routine interval that depends on distance or running hours. It is not a fuel additive, not an oil additive, not an ECU remap and not a retrofit — nothing is introduced into the fuel or oil systems, and no hardware is changed. We do not explain here how a coating on a filter would change combustion: that is the manufacturer’s proposed mechanism, and we have not independently measured it.

Across 17 results — supervised trials and operator records, which we rank below them — 71% show consumption reductions between 5% and 15%, with a median of 10.7%. That is an observation across a specific set of trials. It is not a level of performance we promise. Some individual trials were weak, and some were mixed or inconclusive. The weakest is a Nigerian generator fleet, IHS Towers, running continuously at near-zero load: a small positive median of +1.7%, too small and variable to establish a clear treatment effect for that duty cycle. Results depend on engine type, duty cycle, filter condition and correct application.

Where fuel consumption falls, fuel-related CO₂ falls proportionally, but that is calculated from the fuel burned, not a separately measured exhaust effect. Our field data covers diesel, petrol and LPG vehicles; for HVO, biodiesel and gas we have no field validation and make no performance claim.

Because it requires no retrofit capex and adds no downtime beyond the service, it can be tested on part of the fleet while everything else stays the same — which is also the only way to know what it does on your vehicles. Every trial behind these figures, with its method and its limits, is on our trial results page.

HVO, hydrotreated vegetable oil, is a renewable diesel that can be used where the engine manufacturer approves it. Under the UK government’s 2026 company-reporting factors, the biogenic CO₂ from HVO is set to zero within Scope 1, while methane and nitrous oxide remain in Scope 1; the CO₂ physically released during combustion is reported separately, outside the scopes (DESNZ — accessed 15 October 2026). That is an accounting treatment, not zero CO₂ at the exhaust and not a lifecycle comparison. Fuel use still has to be measured, and the treatment that applies depends on your reporting framework and the supplier’s documentation.

Lower fuel use and a lower reported Scope 1 factor work together rather than compete: a fleet that burns fewer litres needs less fuel of any kind. Availability, price, lifecycle performance and reporting treatment depend on the fuel, its feedstock, the country, the supplier and the documentation. How HVO is treated for carbon prices in each country is shown in our ROI calculator.

1. Baseline. Litres and distance per vehicle, by month, for at least the last year where records allow — the full-tank method and our report template make this routine.
2. The low-capital measures. Driving, tyres, idling, maintenance and routes, introduced one at a time or with comparison vehicles.
3. A pilot of the air-filter treatment on part of the fleet, measured against your own baseline and, ideally, comparable untreated vehicles — our pilot programme is set up for exactly this.
4. The fuel decision. Whether HVO or another renewable fuel is available, approved by your engine manufacturer and worth its price.
5. The numbers for the board. Fuel cost, carbon cost and calculated CO₂ with your own figures — in the ROI calculator — and Scope 1 calculated with the method and factors that apply to your inventory.
6. The replacement plan, vehicle by vehicle as each one becomes due.