Diesel Emissions Versus Gasoline: Which Fossil Fuel Pollutes More?

The simple answer is diesel emits slightly more pollutants per gallon than gasoline does. But, as is often the case, the simplest answer does not tell the whole story with respect to diesel emissions versus gasoline. The reality is, gasoline both emits more emissions and is a greater polluter than diesel.

Nevertheless, the simplest answer is the best place, to begin with, respect to quantifying diesel emissions versus gasoline. To find even the simple — though incorrect — answer as to which of the two fossil fuels produce more emissions, standards of measure and definitions are required. Comparing diesel emissions versus gasoline requires a common unit of measure: gallons. A definition — a list — of emissions is another requirement.

It can be stated almost without dispute that diesel emits a greater sum of emissions per gallon than gasoline. However, in truth, gasoline is a greater polluter than diesel. That fact is equally indisputable. “While diesel fuel contains slightly more carbon (2.68kg CO₂/litre) than petrol (2.31kg CO₂/litre), overall CO₂ emissions of a diesel car tend to be lower. In use, on average, this equates to around 200g CO₂/km for petrol and 120g CO₂/km for diesel.”

And the reason why? A gallon of diesel has far more energy than a gallon of gasoline, yet the amount of emissions each fuel emits upon combustion is only slightly different.

Emissions per Gallon: the False Dilemma

Gasoline emits more emissions than diesel, but not per gallon. However, there is very little value in determining emissions per gallon. By arguing gasoline engines emit fewer emissions than diesel engines because fewer emissions result per gallon is based on the assumption that diesel and gasoline have the same fuel density.

Arguing gasoline emits fewer emissions than diesel because per gallon diesel emits more emissions than gasoline assumes that a gallon of diesel and a gasoline of gasoline produce the same amount of power, that a gallon of the two fossil fuels produces the same amount of work. But that is not the case. The energy produced by a gallon of diesel is far more than that produced by a gallon of gasoline.

In other words what is important with respect to emissions is not the amount per gallon produced. What is important is the ratio of emissions per unit of energy produced.

In other words, if gasoline emits only slightly fewer emissions than diesel per gallon — say 3 percent, — yet gasoline only powers an engine 70% as far or for as long as diesel per gallon, gasoline is, in fact, the greater polluter. “Diesel fuel contains roughly 10% to 15% more energy than gasoline. So, diesel vehicles can often go about 20% to 35% farther on a gallon of fuel than their gasoline counterparts.”

In a few simple steps it is easy to understand why gasoline engines are greater polluters than diesel engines, but again, before it is possible to determine the difference between diesel emissions totals versus gasoline emissions totals, a definition of emissions is required.

Gases the Combustion of Diesel and Gasoline Emits

There are literally hundreds of gases that escape into the atmosphere when fossil fuels burn. However, some are relatively harmless — benign with respect to human health and global warming.

Others, however, are tremendously toxic or have extremely high global warming potentials. But, many toxic and dangerous gases are not worth a great deal of concern because of the relatively small amount produced during fossil fuel combustion. The amount is so minuscule, discussing these gases does very little except confuse the issue with respect to truly damaging and dangerous emissions gases.

There are six (6) gas emissions from diesel and gasoline that have a dramatic effect on global warming and the environment as well as human health conditions.

Carbon Dioxide and the Non-Toxic, Benign Greenhouse Gases

There are three principal emissions from vehicles and machines that are benign when people come into contact with them. But, these three emissions are substantial contributors to global warming and climate change. Though there are other gases produced during human activities that have a greater effect on global warming, these are the three most damaging greenhouse gases produced from diesel and gasoline combustion.

Carbon Dioxide (CO2)

The most well-known greenhouse gas that results from fossil fuel combustion is carbon dioxide. Carbon dioxide occurs naturally in the atmosphere. It is a byproduct of non-human activities like lightning-strike forest fires, eruptions from volcanoes, and biological emissions from the oceans. Nonetheless, CO2 is the greatest contributor to global warming of all gases produced from human-related activities.

That is not to say CO2 is the most potent greenhouse gas (GHG), however. There are many other GHGs with higher global warming potential, but CO2 is the gas produced in the largest sums.

Nitrogen Gas (N2)

There is some debate as to whether or not nitrogen gas should be considered an emission. The total composition of the atmosphere is 78 percent is nitrogen. Most of the nitrogen gas that escapes into the atmosphere following fossil fuel combustion is merely nitrogen gas that already existed, N2 that was sucked into an engine through the air intake and passed through the engine unchanged.

Still, N2 is a greenhouse gas. And, N2 is a greenhouse with a high global warming potential. Though small amounts, N2 is a byproduct of fossil fuel combustion engines.

Water Vapor (H2O)

Though one would think water vapor in the air is a good thing, water vapor is a major contributor to global warming. Of the two major chemical changes that the hydrocarbons — hydrogen and carbon chemical compounds — found in fossil fuels undergo is a conversion into water (hydrogen and oxygen chemical compounds) during combustion.

The global warming potential of water vapor is XXX times that of carbon dioxide.

Toxic Greenhouse Gases Produced in Large Quantities during Fossil Fuel Combustion

Again, there are a large number of greenhouse gases that are very toxic, but that is not produced in large quantities. However, there are three that are both toxic and are produced in large quantities during fossil fuel combustion.

Carbon Monoxide

A colorless, odorless gas, carbon monoxide is both a greenhouse gas with global warming potential as well as a toxic gas that harms humans and animals. Exposure to small amounts of CO leads to headaches and nausea. Exposure to large amounts can cause heart attacks and death in animals and humans.

Carbon monoxide is not a direct greenhouse gas. Unlike CO2, CO does not have a high global warming potential. However, CO does interact with hydroxyl radicals (OH) and make them inert. Hydroxyl radicals are positive gain agents in the atmosphere because they break down greenhouse gases like CO2 and methane.

When CO destroys OH radicals, those radicals can’t reduce the global warming effects of greenhouse gases with high global warming potential.

Nitrogen Oxides

The effects of oxides of nitrogen — nitric oxide and nitrogen dioxide — include inflammation of the airways and other respiratory issues. Moreover, while nitrogen oxides do not have a high global warming potential, “NOx gases react to form smog and acid rain as well as being central to the formation of fine particles (PM) and ground-level ozone, both of which are associated with adverse health effects.”

Hydrocarbons, AKA, Volatile Organic Compounds (VOCs)

Because no engine is capable of capturing 100 percent of the potential energy in a fossil fuel — meaning no engine burns all of the fuel that passes through it — unburned fuel escapes into the atmosphere. Smog is nothing more than vaporized, unburned fuel molecules.

Vaporized, volatile organic compounds have proven to cause cancer in animals and are suspected of doing the same in humans. According to HealthLinkBC, “VOCs include a variety of chemicals that can cause eye, nose and throat irritation, shortness of breath, headaches, fatigue, nausea, dizziness, and skin problems. Higher concentrations may cause irritation of the lungs, as well as damage to the liver, kidney, or central nervous system.

Some VOCs are suspected to cause cancer in humans and have been shown to cause cancer in animals. The health effects caused by VOCs depend on the concentration and length of exposure to the chemicals.”

There are, of course, many more greenhouse gases. Methane, for example, is probably the most potent greenhouse gas on Earth and constitutes between 90 to 98 percent of natural gas. But, with respect to diesel and gasoline fuel combustion, carbon dioxide, nitrogen gas, and water vapor have the highest global warming potential. Carbon monoxide, nitrogen oxides, and hydrocarbons

Emissions Types and Amounts from Diesel and Gasoline Emissions

Not taking into account technologies that reduce emissions — namely, catalytic converters, — gasoline pollutes far more than diesel when the two combust. As AirQuality.Org explains, “Diesel fuel contains more energy per liter than petrol and coupled with the fact that diesel engines are more efficient than petrol engines, diesel cars are more efficient to run. Diesel fuel contains no lead and emissions of the regulated pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) are lower than those from petrol cars without a catalyst.”

Again, petroleum-powered engines without catalytic converters produce large sums of carbon monoxide, hydrocarbons and nitrogen oxides. Diesel engines do not.

Fuel and Emissions Technologies Reduce Emissions Dramatically

Without fuel and emissions technologies, the combustion of gasoline produces less power than diesel, more emissions, and emissions that are more toxic. But with the advent of the catalytic converter, that changed. Though catalytic converters reduce emissions, there is a tradeoff. Catalytic converters cause vehicles to run less efficiently, use more gasoline, and produce greater sums of CO2.

“Emissions from petrol cars have been dramatically reduced by the introduction of catalytic converters, which oxidize pollutants such as CO to less harmful gases such as CO2. When compared to petrol cars without catalysts, catalyst cars have much lower CO, HC and NOx emissions, at the expense of CO2 emissions, which increase due to the oxidation of carbon monoxide to CO2.”

Diesel engines, again, however, produce low quantities of carbon monoxide, hydrocarbons and nitrogen oxides are low.

And, diesel fuel technologies like fuel catalysts reduce emissions even more. The Rentar Fuel Catalyst reduces carbon monoxide, carbon dioxide, nitrogen oxides, and sulfur dioxide by 19.2%. In other words, just as technologies reduce the number of emissions produced by gasoline, diesel fuel technologies reduce the number of emissions from diesel combustion.

Equally as important as the fact that diesel fuel catalysts reduce emissions is the fact that they increase fuel efficiency. Unlike the catalytic converters on gasoline-powered vehicles that actually decrease fuel efficiency, pre-combustion fuel catalysts increase fuel economy.

The Rentar Fuel Catalyst, for example, increases off-road equipment fuel efficiency by between 3 and 8 percent. The Rentar improves the fuel economy of stationary generators by between 7 and 12 percent. Over the road vehicles, in addition to a huge reduction in emissions, gain between 2 and 5 percent in fuel economy. In marine applications, the increase can be up to 10 percent. The Rentar increases the fuel efficiency of boilers and furnaces by between 7 and 30 percent.

No Argument for Favorability of Gasoline Engines Over Diesel with Respect to Emissions

Especially taking into account the technologies that reduce diesel emissions — emissions data results for gasoline engine emissions is almost always taken from tests on vehicles with catalytic converters as catalytic converters are an international requirement for vehicle manufacturers — the diesel emissions versus gasoline is hardly a debate.

Diesel engines run cleaner and more efficiently than their gasoline counterparts.


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