When I started at my last job, in 1978, I attanded an in office talk on emissions:

Smoke: It has neither mass nor volume. It does not contribute to combustion inefficiency. It is an optical effect and very difficult to measure. The measurement techniques did not correlate. Smoke levels could not be predicted with any certainty. The fuel in question was standard aviation kerosene.

When I left work 30 years later, the above was exactly the same.

One thing is true though, any smoke from any jet engine is unacceptable. (You can answer why).

JA

EU emissions standards.

Comparing Euro 6d level emissions of petrol and diesel engines of passenger cars.

Units grams/km

Petrol  CO 1.0

Diesel  CO 1.0

Petrol Nox   0.060

Diesel Nox   0.080

Petrol particulates 0.0045

Diesel particulates 0.0045

There is no cognisant reason to blame Euro 6d level diesel engines for excessive pollution.

On 28 January 2026 at 23:00 howardb Said:

EU emissions standards.

Comparing Euro 6d level emissions of petrol and diesel engines of passenger cars.

Units grams/km

Petrol  CO 1.0

Diesel  CO 1.0

Petrol Nox   0.060

Diesel Nox   0.080

Petrol particulates 0.0045

Diesel particulates 0.0045

 

There is no cognisant reason to blame Euro 6d level diesel engines for excessive pollution.

 

 

 

 

 

If this is the case, maybe it’s emissions compliance that should be scrutinized, not the fuel itself?

On 28 January 2026 at 20:04 JA Said:

When I started at my last job, in 1978, I attanded an in office talk on emissions:

Smoke: It has neither mass nor volume. ..,

That’s an unusual definition of smoke!  Who was the source?  Not citicising! Although engineering tries to standardise terms, history is against us.  For fun, how many different technical definitions of “thread” are there?  “Smoke” is also likely to have multiple meanings.

Chemists define smoke as an aerosol of fine particles (less than ⌀1μm) mixed with combustion products, mainly gases and vaporised hydrocarbons.   The gases typically include Carbon Dioxide, Carbon Monoxide, Nitrogen Oxides, Cyanides, and maybe a whiff of Dioxin!  All the constituents of smoke have mass and volume, which can be measured.

The “neither mass nor volume” confusion may be that the mass and volume of smoke is much the same as air, so not obvious.   The key point is that Smoke is far from harmless/   Small quantities trigger asthma attacks, and cause minor damage to lung tissue that can be infected (Bronchitis etc), and sometimes spark cancerous changes.  Smoke inhalation is the most likely cause of death in fires.

The enquiry into the Grenfell fire revealed shocking shortcomings in UK Building and Fire Regulations, the latter being badly out of date. Resulted in this paper:  ” Research and analysis Fire safety: Smoke and toxicity“.  Published 22 December 2025, not nearly 50 years ago, and I suggest is more trustworthy than JA’s version.

On 28 January 2026 at 23:00 howardb Said:

EU emissions standards.

Comparing Euro 6d level emissions of petrol and diesel engines of passenger cars.

Units grams/km

Petrol  CO 1.0

Diesel  CO 1.0

Petrol Nox   0.060

Diesel Nox   0.080

Petrol particulates 0.0045

Diesel particulates 0.0045

 

There is no cognisant reason to blame Euro 6d level diesel engines for excessive pollution.

 

Not sure what Howard’s table is.  Are they emission targets measured steady-state in a lab?  Well-known problem with steady-state lab results, because cars on the road are far from steady-state. This table summarises real-world Urban Cycle performance from various sources.   As the numbers are much less rosy than those in Howard’s table, there is cognisant reason to blame diesel engines for excessive pollution!

Real-road and lab test numbers both show petrol engines produce more CO₂ than diesels.  As CO₂ is causing climate change, a major threat to humanity in the mid and long term, UK government encouraged drivers to go diesel, only to discover a major problem a few years later.  Trouble is diesel’s produce much higher levels of particulates and Nitrous Oxides than petrol engines, and these bery obviously reached dangerous levels in town centres and confined spaces.  About turn!

Though IC engines have been considerably improved over the last 40 years, electric is the best answer to local toxicity and global warming at the moment.  I think all that can be done to improve IC engines has been done, such as:

• cleaner combustion. Fuel-injection, improved mixing in the cylinder, plus sensor enabled timing and other tweaks provided by microcontroller based engine management units
• Removing Lead from petrol.
• Catalytic Converters on petrol exhausts turn toxic Carbon Monoxide into Carbon Monoxide, consume unburned fuel and soot, and reduce some Nitrous Oxides too.
• Much better particulate filters on diesels, but effectiveness depends on how the vehicle is driven and maintained.   Room for improvement maybe, but not obvious how.

I’m not against diesels used sensitively, and big diesels are less damaging than small ones (more time and space in big cylinders to complete combustion).  Railways, long-distance road-haulage, agriculture, heavy earth-moving, and maritime.  Allowing thousands of small diesels to chug and queue in busy town centres is harmful.   They have to go…

Dave

Something that sticks in my mind from the late 70s, when the push was for people to buy diesel cars rather than petrol, was the statement in Car Mechanics magazine: “Diesel fumes are not carcinogenic.”

Truth changes over time.

Rob

The talk I attended was in the late 70s. The smoke to air was considerably lower than road going diesel vehicles and was no carbon but heavy poly-cyclic aromatics. As aromatics it was considered carcinogenic and a major risk to health. The talk then went on to the “lab rat test” and how such tests with distilled water had shown that it was carncinogenic.

Dave, we were not chemists but combustion engineers. We had to try to undrestand the stuff (how it is produced and removed in a contunuous flow constant pressure combustion system), not just the chemistry. The other emissions were far easier.

JA

The figures I quoted are the EU emission standards for Euro 6b passenger car diesel engines.

The reason for choosing that particular standard was to demonstrate that a modern diesel engine is very close to the level of emitted pollutants of a comparable petrol engine.

Also chosen as it’s the emission spec for my newest car which uses Adblue, powered by a Renault K9K 1.5 litre 115 hp 4 cylinder diesel.

“When AdBlue is put into the exhaust system, it gets hot. The higher temperature creates a reaction with the exhaust gases that degrades the mono-nitrogen oxides that are harmful. During this process, the gases are converted into water (H2O) and nitrogen (N3), both of which are harmless to people and the environment. In total, it filters out over 90% of the harmful emissions”

What is AdBlue and Why Do Diesel Cars Need It?

On 29 January 2026 at 19:01 Fulmen Said:

They are just nice, comfortable cars. Plenty of smooth torque from stationary, no gears, no noise, no oil and fluids you forget to check, little noise and cheap to run.

If you think EV’s have no gears, oil or fluids you have been mislead.
They have gearboxes which contain oil and the motors, electronics and sometimes often the batteries use liquid coolant.

A significant disadvantage is how you charge them if you don’t have a driveway or similar.

Robert.
(Been running a PHEV for 6 years now and helped build the most fuel inefficient car in history, about 35 gallons per mile on kerosine.)

its a newspaper article so perhaps an interpretation by the journalist rather than accurate facts?

There has been a glut of petrol in the country (UK) and a (relative) shortage of diesel fuel.  The UK has been exporting the excess petrol and buying in diesel.

Has the journalist picked up on this?  Perhaps its more noticeable in the London area than elsewhere?