Gasoline Engines Emit More Particulates Than Diesels


For years, the conventional wisdom has been that pollution from diesel engines was far worse than from gasoline engines for two reasons: First, diesel exhaust fumes are known to contain nitrous oxide emissions. Second, they also contain particulates, small molecules that are too small to see. Both are believed to cause serious damage to human lungs.

Direct Gas Injection Increases Particulates In Gasoline Engines

Particulate Emissions From Gasoline Engines

Now it turns out that conventional wisdom is wrong. A study by researchers at the Materials, Science, and Technology Laboratory in Switzerland claims that particulate emissions from gasoline engines can be far greater than those from diesel engines.

The laboratory studied the emissions of 7 gas engine vehicles equipped with direct-fuel-injection systems. The research found that they emit from 10 to 100 times more particulates than modern diesel engines. In fact, they have higher particulate emissions than older diesel without particulate filters.

Wait, did you read that right? Gasoline engines spew out up to one hundred times more particulates that a modern diesel engine equipped with a particulate filter? Yes, you read that right.  Yikes. And people wonder why the incidence of asthma and other lung related diseases is on the rise!

Researchers Find Carcinogens In Gas Engine Exhaust

The researchers, led by Norbert Heeb, who has 25 years of experience analyzing emissions from diesel engines and designing filter systems, showed that the particles are the same size as those from older diesel engines. They measure between 10 and 20 nanometers and clump together into particles between 80 and 100 nanometers before they leave the exhaust system.

The gas engines were also found to discharge unburned hydrocarbons in the form of polycyclic aromatic hydrocarbons (PAHs), along with other liquid and solid toxins which accumulate on the surface of the emitted particles.

Particulates Penetrate The Lungs

Heeb says the particles are so small they penetrate lung tissue and pass into the bloodstream, bringing those toxins with them. Is this beginning to sound like the days when researchers first told the world about all the nasty stuff contained in cigarette smoke? It should, because it turns out there is a connection to smoking. The researchers also found that the exhaust gasses coming out ot the tailpipes of the cars with gas engines also contain benzo-α-pyrene, a carcinogenic produced when tobacco is burned.

A Call For Particulate Filters

He urgently suggests that carmakers begin equipping their gas-powered cars with particulate filters. “New exhaust emission technologies launched on the market typically need about 13 years to become fully effective. Only after that period of time will 9 out of 10 cars in the vehicle fleet be replaced,” he says. “So, the faster particle filters are mandatory in gasoline cars, the better it will be for everyone’s health.”

Direct Injection Is The Cause

The culprit in all of this appears to be direct-injection systems themselves. Gasoline engines do not inherently form particulates in the exhaust. In older electronic fuel injection systems with an injector located in the intake tract, fuel is added at the end of the exhaust stroke as the piston is travelling away from the combustion chamber.

In direct injection engines, the fuel is added as the piston is headed back toward the combustion chamber after the end of the intake stroke. This gives the fuel less time to evaporate, claims Heeb, which results in more more unburned hydrocarbons, which means more soot.

Direct injection allows more precisely controlling the fuel delivery process, leading to better fuel economy and lower carbon dioxide emissions. Apparently, few people have tested gas-powered cars equipped with direct-injection systems for anything other than CO2 until now.

Another Reason To Go Electric

What’s the bottom line? Just this: Thanks to the Swiss researchers, now we know that our cars are slowly killing us and the planet we live on. It is time to end the reign of the internal combustion engine and push forward with the transition from fossil fuel cars to zero-emissions electrics. Our health depends on it.

Source: TU Norway | Photo Credit: Bosch

Hat tip to Leif Hansen. 

About the Author

I have been a car nut since the days when Rob Walker and Henry N. Manney, III graced the pages of Road & Track. Today, I use my trusty Miata for TSD rallies and occasional track days at Lime Rock and Watkins Glen. If it moves on wheels, I'm interested in it. Please follow me on Google + and Twitter.
  • James Rowland

    I’ve been saying for a while that the demonization of diesel is a failure of perspective that’s been distracting us.

    Combustion in general is what’s denying us clean air, it can’t be made clean and the sooner this is recognised by the public the better.

    (Oh, and yes, people who inhale combustion products deliberately are fools.)

    • Steve Hanley

      Precisely. The howling mob that has been demonizing Volkswagen for filling the skies with harmful NOx emissions is right to be incensed, but they are focusing all their anger on 0.007% of the problem. Internal combustion engines are a far greater threat to human health than cigarettes ever were.

  • Epicurus

    Good to know.

    It’s like the furor over fracking. The problems caused by fracking pale in comparison to the problems caused by the very drilling of oil and gas wells, fracked or not. It is estimated that about 20% of all wells will develop casing leaks which then cause of fresh water pollution. Drilling needs to stop. Period. Best way to get there: buy an electric car and decrease demand for oil.

  • MeatBoy

    Hum… How can you be so sure that your electric cars are that green ? Because draining a battery is harmfull and that’s it ?
    Massive batteries do not fall from the sky but require very pollutant raw material and heavy industrial transformations. Lithium almost exclusively comes from China BTW. I don’t hate China but I don’t want to depend on them for that either.
    Also the electricity supply can’t keep up with millions of cars loading at the same time, especially during winter, unless we fire up the coal, gas and oil power plants.
    Finally, road erosion and tires and brake pads wear are responsible for a significant share of the overall particulates emission. That will be even more true once the particulate filters will be installed on gas engines, which will be the case in less thant 1 year for new vehicules.
    Electric cars are good only if not used by to many people. Hybrid might be the way to go for the coming years.
    PS: Have a look at the EQUA air quality index. Its conclusions are not as worrying as that about modern turbocharged DI downsized gas engines when compared on the same basis as DPFed diesel engines

    • SenseWillPrevail

      “Also the electricity supply can’t keep up with millions of cars loading
      at the same time, especially during winter, unless we fire up the coal,
      gas and oil power plants.”

      EVs do NOT all charge up at the same time. That’s like suggesting everyone who has a torch/flashlight will SIMULTANEOUSLY plug them in to recharge, regardless of the stae of the batteries; full, three-quarters full, half-full, etc.

      Designers/engineers are actually designing batteries so that they can give INTO the national supply when maximum power is needed (e.g. when evening/holiday meals are cooking) and recharge (say) overnight when less power is used nationally. So batteries will be more solution, less problem.

      Even if that proves optimistic, the solution is NOT to ” fire up the coal, gas and oil power plants.” – renewable sources can provide more than enough energy to meet the world’s needs.

      • MeatBoy

        Well, I can’t say that you are wrong… I even have to say that I like the future you are describing. But thinking a great future is very different from achieving the transition from our reality to this future.
        As far as I can see, switching to electric cars ‘right now’ is a bad idea. They currently simply can’t send back their juice into the grid ; they will likely load at night when people come back home for most of them asking for a huge additional amount of power at critical hours ; the number of public chargers is ridiculously low (here in France at least) which emphasizes the last issue ; the battery technology improvement is throttling (a lot of magical promises for years now but no functional product so far) and a major change is required to compete with gas convenience.
        I also hope that you realize that the renewable sources of energy are currently far from being able to keep up with the demand on a regular basis, even without having to charge to many electric cars. That means that increasing significantly the demand will likely result in coal/gas produced electricity. I let you do the math then : burning a combustible in a power plant has a slightly better efficiency than burning it in an engine (but not much better because of thermodynamics constraints) ; transporting electricity through the grid induces roughly 10% lost on average ; charging and discharging a battery loses roughly another 10% ; converting CC to three-phase AC and then spinning the motor loses another 10% (maybe a little bit less). In the end you did not save the planet. This stands only for today and the coming few years. Let’s then see what engineering has to offer.

        And just as a bonus : if one has an electric car, then I have a heat car (the final energy which powers the engine) ; if one has a redox car, then I have a combustion car (the chemical process which converts the energy from its storing form to its usable form) ; if one has a battery car, then I have a gas tank car (the energy storing device). But it is very likely that, in the end, we both have a fossil primary energy source car, and that is what matters. Electricity is not clean to produce and there is much to do to make that statement wrong.
        But don’t get me wrong, “electric” cars with clean batteries, clean power production (and powerful enough) is the best I can think of right now. It just doesn’t exist and hybrid (actually any efficient braking energy recovery system) is the best from an ecological point of view so far.