Ad: How Cambustion’s testing is helping to advance the air quality movement

When it comes to air quality, testing and monitoring is vital for tracking pollutant emissions and their effects on low-emission zones.

Mark Peckham, Director at Cambridge-based Cambustion, talks to Air Quality News about the work the independent testing company is doing and why it’s important.

What is Cambustion and what prompted the company’s launch?

Cambustion is the inventor and manufacturer of ultra-fast response gas and particulate analyzers – a spin-off company from the University of Cambridge engineering department in 1987. At that time, emissions limits and catalytic converters were relatively new in Europe and their control was the subject of much interest and conventional analyzers were too slow to study transient engine behaviour, such as cold start.

Cambustion’s niche is that its analyzers have millisecond response times specifically to be able to measure the products of combustion from each and every exhaust stroke – useful when modern engine control units have the ability to deliver exactly the right amount of fuel for stroke number one, and then a different amount for stroke number two etc, as well as hundreds of other parameters which affect emissions. We are, therefore, suppliers to engine manufacturers large and small, for example Ford, General Motors, Chrysler and Mazda. We also provide testing services to optimise combustion and catalytic converter systems and make the exhaust gases as clean as possible. This involves the use of our engine test rooms, rolling roads and big motors to which engines can be connected and simulate driving a complete vehicle on a variety of drive cycles and in a range of conditions, including freezing. We therefore have in-depth background knowledge of how engines and exhaust catalyst systems work and what might cause them to fail!

When did Cambustion first start testing air pollution?

When we were in the spring of lockdown, we were developing a portable version of our fast NOx analyzer and to maintain social distancing and good ventilation, we were working outside in the fresh air near our ‘goods-in’ door. We began to notice that with many visiting courier vans, we were picking up a tell-tale signal from their NOx tailpipe pollution as they drove past.

After a little more optimisation of the equipment, we realised that we had sufficient sensitivity and, crucially, very fast time response to discern the NOx in the plume of each and every passing vehicle. Clearly some were cleaner than others and as the days wore on, we could build up a picture of those vehicles which were higher polluting.

We then moved to a roadside location, recording the scene with a simple dashcam and found that we could correlate the roadside air quality with the number plates of each passing vehicle. Typically, over a 30 minute period, there would be 4-6 vehicles which have spikes associated with them of perhaps 100 times the mean level.

Vehicles which emit high levels of NOx, could be doing so legally, such as old vehicles or the auxiliary diesel-engined power units which drive refrigeration systems. However, there is a growing awareness of tampering with diesel-engined vehicles which are relatively new and are fitted with the latest NOx reducing catalyst systems (SCR systems which take urea “Adblu” fluid). There is an abundance of ’emulators’ on the market aimed at both business and private diesel vehicle owners which defeat the SCR system rendering it inoperative and yet suppressing all warning indications which would otherwise fail MOTs.

The emulator suppliers often claim not only savings in Adblu consumption and SCR maintenance costs, but improved fuel economy based on the disabling of catalyst heating strategies.

We’ve since worked with local authorities, national governments and helped the UK enforcement agencies to identify these ‘gross emitting’ vehicles based on rapid detection of each passing vehicle’s exhaust plume NOx content. Using ANPR, we can identify each vehicle’s emissions classification.

An additional important feature of this technique is its portability at under 20kg: the equipment is housed within a pull-along suitcase and can therefore ‘pop-up’ at any roadside location or can be carried inside a pursuit vehicle with the sample pipe measuring the tailpipe plume of the vehicle in front.

Why is it important for air quality to be tested and monitored?

California Air Resources Board (CARB) indicate that 50% of truck NOx emissions are caused by only 3.9% of such vehicles. This is a good illustration of the large improvements in air quality that could be made simply by identifying and rectifying a relatively small number of vehicles (gross emitters).

This is borne out by the typical data we record at most roadside locations where only a low % of vehicles appear to produce very high NOx spikes and thereby skew the local air quality.

Projects which we have undertaken for some local and national governments focus on identifying the reasons why a particular urban location may be experiencing unusually high levels of NOx – often after measures have already been taken to tackle this.

So-called NOx ‘hot-spots’ tend to occur near traffic intersections where the vehicles are accelerating away from a set of lights. Speed bumps are also good at aggravating NOx from otherwise clean vehicles as the periodic deceleration and acceleration upsets their emissions control systems.

Clearly, the adoption of Clean Air Zones allowing entry of only Euro 6 vehicles would be severely compromised by the use of emulators fitted to such vehicles; their entry being allowed purely on recognition of their Euro status on the basis of their number plate.

There are also less controversial reasons why normally clean vehicle may emit high NOx: if they are starting after several hours of rest, there is a start-up transient spike of NOx while their catalyst systems warms up to its activation temperature. One can therefore imagine that downwind of a large car park or a large vehicle depot, the ambient NOx may be elevated.

City geography and topography may also be a factor: for example, an air quality monitoring site at the foot of a hill next to a traffic intersection can prove troublesome because as vehicles drive downhill their engines often go in to ‘decel fuel shut-off’ where no fuel is injected and the engine simply turns over without combustion. The adverse effect here is that the cold air flow through the engine and exhaust therefore cools down the catalyst and causes it to be inactive at the time when the engine restarts to pull away from the intersection.

Portable monitoring work like this can also sometimes reveal some inconvenient truths. Sometimes it can be a council’s own vehicles which are the largest emitters. On a recent walking test from a

transport hub to the front of a children’s hospital, the highest NOx levels were found to be from idling ambulances at the hospital entrance.

Where do you see Cambustion going in the future?

As part of our diversification away from raw engine emissions measurement, we now have various medical clients who study individual inhalation and exhalation events and the nitric oxide (NO) contained therein. NO is administered as a vasodilator in respiratory medicine and its accurate dosage is important. The ability to improve NO delivery systems and minimise formation of NO2 within oxygen cannulas is driving some of our current sales. The development of fast CO2 measurements with which to normalise the measured plume dilution is also currently being finalised.

But we find our engines background remains useful and relevant in the interpretation of air quality projects. We know ‘what makes engines tick’ and can thereby provide reasonable assumptions as to why particular monitoring positions might be subject to high levels of pollutants.