In response to reports that he had died on a trip to Europe, Samuel Clemons, known to the world as Mark Twain answered that “the report of my death was an exaggeration”. While the title of this post is also an exaggeration, the truth is that civil society is in the process of changing its mind about the relative merits of diesel versus gasoline cars and the winner in the current debate is likely to be Nissan, Tesla and other companies launching battery electric vehicles in the coming years.
Engineering
The essential difference between a gasoline engine and a diesel engine is that gasoline is ignited by a spark club while a diesel engine uses pressure to cause the fuel to explode. It is the explosive force in both cases that moves the pistons and eventually the car.
The different types of combustion means that the fuels are different and the resulting fuel economy and exhaust emissions are not the same.
The good news is that diesel engines get more power from less fuel so that a diesel car will use less fuel and also and produce less carbon dioxide for the same trip as a gasoline powered car. The bad news is that the explosion is not as complete and the resulting exhaust emissions have significantly more Nitric Oxide (NO) and Nitrogen dioxide (NO2) than gasoline engines and also produce more soot, or particulate matter, that is loaded with toxins.
The NO and NO2 can produce harmful ground level ozone and the particulates are so small they can penetrate people’s lungs and do serious damage.
History
Another problem with diesel engines is that for the same size and weight they traditionally produced a bit less power and made more noise. That changed in the 1990s when the German car companies began introducing new diesel engines which operated at much higher pressures and were more powerful and quieter.
European governments embraced the technology initially to reduce the overall volume of imported oil and later as a way of meeting ambitious goals of carbon reduction.
In the U.S. the technology never really moved from trucks (which are all diesel) to cars largely because the first mass market vehicles sold, such as the VW Rabbit, were considered slow, noisy, and smelly.
Diesel engine’s can be made to run cleaner by treating the exhaust for NO and NO2 and filtering out the particulates using technology that has been developed for that purpose over the last few years. The problem is that the pollution control equipment adds weight and cost to the car and also takes away some of its performance.
In order to make their cars fun to drive and also to pass the increasingly stringent air quality standards, Volkswagen deceived its customers and the regulators by building software into some of its engines would only switch on the pollution control equipment when the car was being tested.
A Tipping Point ?
One result of European policy has been to increase the percentage of diesel powered passenger cars on the road to about 50% across Europe. At the same time, congestion has increased in many European cities and the combination of these two trends is producing an air quality crisis.
To give a sense of the importance of the issue, last week, the BBC asked me to talk about the issue and the event attracted 140,000 people on Facebook live! What you could see in the questions and comments during the show was that a portion of civil society wants cleaner air.
A Matter of Time
The problem is that despite significant incentives in many places, consumers have not yet begun to buy electric vehicles anywhere but in Norway where they represent about 30% of new car sales.
Since my last post on EVs in 2014, worldwide sales have increased but are still less than 1% of the global automotive market if one only considers vehicles which go over 80 Km/Hr.
The issue with EVs is that they are only cleaner on a global basis than gasoline or diesel cars if the energy mix itself is cleaner. An electric car in London, for example, makes about the same amount of pollution and carbon as a high end hybrid.
What is different from an air quality point of view is that EVs allow a society to move the point of pollution away from the city center to wherever the power plants are located.
While they will not save the planet until there is a complete transformation of the energy system, they could very quickly improve the air in many cities around the world potentially saving lives and reducing health care costs.