Every fossil fuel is a composition of different hydrocarbons. The most toxic emissions of gasoline and diesel are not the same. As a result, different fossil fuels burn differently. Different fossil fuels combust at different temperatures and at different rates of efficiency. And, every fossil fuel produces different rates emissions. 

And, just as every fossil fuel is different, so too are the emissions from those fossil fuels. Some emissions from the combustion of fossil fuels are innocuous. Other emissions are toxic and poisonous.

Fossil fuels are mixtures of different hydrocarbons. Hydrocarbons are molecules made of hydrogen and carbon atoms. Mixed with oxygen and exposed to heat, hydrocarbons combust to create energy. Combustion — the production of energy — is the result of the breaking of the bonds between hydrocarbon hydrogen and carbon atoms. But, there is a second stage of combustion, the bonding of the free hydrogen and carbon atoms with oxygen. Those bonds — water and carbon dioxide — produce emissions.

Under ideal circumstances, the only emissions from the combustion of fossil fuel would be carbon dioxide and water.

Fossil Fuel Combustion Never Ideal

Because there are contaminants in fossil fuels, combustion engines create a large number of emission types. For one, air is not only oxygen. Air also contains a number of other gas-state elements. In fact, the majority of air — 78 percent — is nitrogen. Only 21 percent of air is actually oxygen. The remaining 1 percent air is made of trace elements. 

As a result, nitrogen composes the vast majority of all fossil fuel emissions. For combustion engines, boilers and stoves that burn a lean mixture, oxygen is another emission. The reason being, in a lean fuel mixture, there is an excess of oxygen. 

In addition to carbon monoxide, water, nitrogen and oxygen, there are trace emissions. Trace emissions generally account for less than three percent of total emissions. However, trace emissions can have a substantial impact.

Not All Emissions are Equal

Some emissions are far worse than others with respect to their effect on the environment and human health. While many of the emissions of different fossil fuels are the same — carbon dioxide and water, for example — each fossil fuel also produces emissions unique to their combustion qualities. Equally important with respect to the production of emissions are the types of engines, stoves, furnaces, and boilers that combust different fossil fuels. 

And again, every fossil fuel produces different trace emissions.

Most Toxic Emissions of Gasoline and Gasoline Engines

No fossil fuel undergoes more refinement than gasoline. In addition to intense refinement, no fossil fuel contains more post-refinement additives. So, the emissions produced by gasoline are more diverse than those produced by other fossil fuels. In addition to the chemical composition of gasoline, gasoline engines are different than other combustion mechanisms.

Carbon Monoxide Most Abundant Trace Emission Produced by Gasoline Engines

Carbon monoxide is the most dangerous and the most abundant emission produced by gasoline engines. And carbon monoxide is one of the most dangerous emissions that exists. “There is no question that carbon monoxide is a pollutant with the potential to harm all living things,” explains the Earth System Science Education Alliance. 

While carbon monoxide does not affect plants, it is extremely harmful to animals. “The toxicity in humans and animals is caused by the extraordinary affinity of carbon monoxide for hemoglobin which is responsible for the oxygen transport (approx. 250 times greater affinity of carbon monoxide compared to oxygen).”

Carbon monoxide can only enter the body through inhalation. It is an odorless and colorless gas. It is not possible to see, smell, or taste carbon monoxide. Nevertheless, with respect to human and fauna life, it is possible the most dangerous of all emissions. Even in small amounts, inhaling carbon monoxide can be fatal. “Acute poisoning takes the form of headaches, retching, muscular weakness, loss of consciousness, shortness of breath and finally death, depending on the concentration and time of exposure.”

Hydrocarbon Emissions Also a Major Concern with Respect to Gasoline Engines

There is a major flaw in gasoline engines: gasoline engines burn gasoline. The problem with gasoline engines is that they can not burn all the gasoline-fed into them. To clarify, gasoline engines can burn all the fuel fed into them, but doing so damages the engine. The perfect mixture of air to gasoline is called the stoichiometric ratio. The stoichiometric ratio is the right amount of air to burn all the fuel in a mixture. For gasoline, the stoichiometric ratio is 14.7 to 1: 14.7 parts air to 1 part gasoline. 

But, a gasoline engine can not run at the stoichiometric ratio. A gasoline engine that runs at the stoichiometric ratio will overheat and seize. In order to prevent engine temperatures from getting too high, gasoline engines must run rich. A rich mixture has an excess of gasoline and a deficit of air. Gasoline engines running rich are air-starved. There is not enough oxygen to burn all of the gasoline. 

Stoichiometric Ratio

Typically, the ratio of air to gasoline in a gasoline-powered engine is about 12 parts air to 1 part gasoline. That is far below the stoichiometric ratio. As such, a portion of the gasoline gets blown out the exhaust — unburned — as hydrocarbon emissions.

“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.”

Until gasoline engines have the capacity to run at the stoichiometric ratio, hydrocarbon emissions will continue to be a major issue.

Aromatic Hydrocarbons — Octane Boosters — May Be Worse Gasoline Engine Trace Emission of All

Again, the biggest problem with gasoline engines is that they burn gasoline. In part, how gasoline engines combust gasoline determines what emissions they produce. Gasoline engines are spark-fired engines. As opposed to the heat from compression causing gasoline to ignite in a gasoline engine, a spark ignites the fuel. The reason gasoline engines require spark-ignition systems is that of the compression resistance of gasoline. 

Gasoline has a very low compression resistance in relation to diesel and other heavy fuels. Low compression pressures inside an engine will cause gasoline to combust, to auto-ignite. In order to prevent an engine from auto igniting gasoline, engineers must keep the compression ratio low. 

The lower the compression ratio of an engine, the lower it’s thermal efficiency. Thermal efficiency is the amount of energy that goes into an engine that is converted to mechanical work. So, in order to increase the thermal efficiency of gasoline engines, gasoline must have higher compression resistance. In order to increase the compression resistance of gasoline, the octane rating must be higher. 

Refinery chemical engineers increase the octane rating of gasoline with aromatic hydrocarbons. 

Aromatic Hydrocarbons: How Refineries Increase Octane Rating of Gasoline

The aromatic hydrocarbons used to increase the octane of gasoline are the sludge hydrocarbons left at the bottom of a distillation unit. After the hydrocarbons that make gasoline, diesel, kerosene, fuel oil, natural gas, etc. vaporize, there leftover hydrocarbons are called “coke.” It is from coke that engineers take hydrocarbons to add to gasoline to increase the octane rating.

In the past, chemical engineers added tetraethyl lead to gasoline in order to increase its octane rating. “Lead,” however, created negative environmental and health effects. One year after tetraethyllead was banned, the world health organization published a research article titled, “The Worldwide Problem of Lead in Petrol.” The first paragraph explains, “The use of lead as a petrol additive has been a catastrophe for public health. Leaded petrol has caused more exposure to lead than any other source worldwide. By contaminating air, dust, soil, drinking water and food crops, it has caused harmfully high human blood lead levels around the world, especially in children.” 

However, the use of aromatic hydrocarbons may not be any better for the environment nor public health. The reason aromatic hydrocarbons are so dangerous is that, when combusted, they create ultra-fine particulate matter (UFPs). In a 2017 article published in Morning Consult, journalist Davis Burroughs reports, “Members of the scientific community, are concerned that aromatics exist in the environment at unsafe levels. The chemicals get released into the air as nano-sized particles – ultrafine particulate matter, or UFPs – that can be absorbed through the lungs or skin. Studies in peer-reviewed journals like the Journal of Environmental Science and Health, Environmental Health Perspectives and Particle and Environmental Toxicology, have linked these particles from aromatics to diseases ranging from ADHD to asthma.”

In addition to carbon monoxide, hydrocarbon emissions, and aromatic hydrocarbon emissions, gasoline also produces nitrogen dioxide. However, nitrogen dioxide is a much bigger concern as it relates to diesel engine emissions.

Most Toxic Emissions of Diesel and Diesel Engines

Diesel engines produce virtually no carbon monoxide. Diesel engines run extremely lean, so diesel engines produce far fewer hydrocarbon emissions than gasoline engines. And, diesel has a very high compression resistance in relation to fossil fuels like gasoline and natural gas. So, there is no need to increase the octane rating. Diesel, then, does not require aromatic hydrocarbon additives, so it does not produce ultra-fine particulate matter. And since the advent of ultra-low sulfur diesel, diesel engines produce very few sulfur oxides.

Nitrogen Oxides Most Abundant Trace Element in Diesel Engine Emissions

However, diesel engines do produce one emission that is very dangerous: nitrogen oxides. Because the air used to oxygenize diesel fuel is 78 percent nitrogen, it is virtually impossible to prevent the generation of nitrogen oxides. In addition to the fact that nitrogen and oxygen are always present in the diesel fuel mixture a diesel engine combusts, diesel combustion creates extremely high temperatures. A high-temperature environment is ideal for the production of nitrogen oxides. 

In an article titled, “Diesel Engines: Design and Emissions,” John Pignon explains. “The main problem areas for diesel engines are emissions of nitrogen oxides (NOx) and particulates, and these two pollutants are traded against each other in many aspects of engine design. Very high temperatures in the combustion chamber help reduce the emission of soot but produce higher levels of nitric oxide (NO).”

Nitrogen oxides are dangerous both to people and the environment. “Nitrogen dioxide and nitric oxide are referred to together as oxides of nitrogen (NOx). 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.”

Particulate Matter a Minor Diesel Emission Issue

Diesel engines produce particulate matter. However, today’s diesel engines produce far less than those of the past. Just as measures were taken to eliminate the sulfur dioxide emissions diesel engines once produce, measures have been taken to eliminate particulate matter. However, particulate matter is still one of the most toxic emissions produced by diesel engines. 

Particulate matter is the diesel equivalent of gasoline hydrocarbon emissions. It is unburned fuel. But, the particulate matter produced by diesel engines is not a consequence of the necessity to burn a rich fuel mixture. The reason diesel engines produce particulate matter is that diesel is a heavy, dense fuel. Because of its weight and density, it is difficult to oxygenate. 

In order to eliminate particulate matter from diesel engine emissions, it is critical to either hyper-oxygenate the fuel or put a particulate matter filter on the exhaust end of the combustion system. There are several ways to increase the oxygenation potential of diesel fuel. One means is ultra-high pressure injectors. However, the higher the pressure of the fuel injectors, the more wear, and tear on an engine. 

Another means of hyper-oxygenating diesel fuel is with a pre-combustion fuel catalyst. The Rentar Fuel Catalyst, for example, can reduce particulate matter — black smoke — by up to 44 percent. 

Nitrogen oxides and particulate matter are two major issues with respect to diesel engine emissions. However, diesel engines have far fewer emissions issues than gasoline engines. And, the emissions issues associated with diesel engines are easily overcome, at least one of them. It is going to be extremely difficult for automobile engineers to remedy all the issues associated with gasoline engines. 

Gasoline Has Far More Toxic Emissions than Diesel

Diesel produces smaller quantities of emissions than gasoline and a smaller number of emission types. Diesel engines do not produce carbon monoxide. Gasoline engines do. Diesel engines do not produce ultrafine particulate matter because diesel does not require octane boosters. Gasoline, because of its volatility and weak compression resistance, does. Because of ultra-low-sulfur diesel, diesel engines produce fewer sulfur oxide emissions. And, diesel engines produce less carbon dioxide and gets better fuel efficiency than gasoline engines. 

Not only does diesel produce less toxic emissions, but it is also a better fuel than gasoline.