Combustion Engines: Pollution, Causes, And Effects

The invention of the internal combustion engine in the 19th century revolutionized transportation but has also posed a significant environmental threat. Engines that run on diesel or gasoline (petrol) produce greenhouse gases and particle emissions that are harmful to human health and the environment. While diesel engines are more efficient and durable, they produce more emissions pollution because they do not always burn all the fuel they consume. This incomplete combustion results in unburned fuel being released into the atmosphere, causing ground-level ozone which damages crops, trees, and other vegetation. Gasoline engines, on the other hand, may not get enough air into the cylinder for combustion, resulting in carbon monoxide emissions. This article will explore the environmental and health impacts of different types of engines and discuss strategies for reducing their pollution output.

Two-stroke engines are more polluting due to their design, which leads to greater exhaust emissions

Two-stroke engines are more polluting than four-stroke engines due to their design, which leads to greater exhaust emissions. Two-stroke engines combine the compression and ignition phases in one stroke and the intake and exhaust in another. This simpler design results in lower fuel efficiency and increased exhaust emissions, as unburnt fuel and large amounts of soot escape from the exhaust. The simultaneous occurrence of the intake and exhaust strokes means that unburnt fuel inevitably escapes, and as two-stroke engines lack catalytic converters, these emissions go untreated.

Furthermore, two-stroke engines require oil to lubricate the engine's moving parts, and this additional oil creates more pollutants during the combustion process. Specifically, two-stroke engines produce higher emissions of hydrocarbons like benzene, which is detrimental to health. The combustion process in internal combustion engines, including two-stroke variants, also produces carbon monoxide, a toxic gas that inhibits oxygen transport in the blood by binding to hemoglobin.

Additionally, nitrogen oxides are formed during high-temperature combustion, which combine with ammonia and volatile organic compounds to form PM 2.5, a particulate matter of size 2.5 μm or less. These fine particles can easily penetrate the lungs and cause respiratory issues, aggravate pre-existing diseases, and even lead to premature death. The combustion process in two-stroke engines, therefore, has severe health implications.

While diesel engines, which are also internal combustion engines, have improved in recent years due to stricter regulations, older diesel engines still in operation contribute significantly to air pollution. Diesel engines, in particular, produce more emissions pollution due to "incomplete combustion," where leftover fuel is forced out of the combustion chamber during the four-stroke cycle, increasing hydrocarbon emissions.

In summary, two-stroke engines are more polluting due to their design, which results in greater exhaust emissions of unburnt fuel, soot, and additional pollutants from the required oil. This leads to severe health and environmental consequences, highlighting the importance of addressing air pollution caused by internal combustion engines.

Diesel engines are more polluting due to incomplete combustion, which releases more hydrocarbons

Diesel engines are a major source of harmful pollutants. The fuel they consume is a complex mix of petroleum components, which, when burned, produces a range of harmful emissions. Notably, a small amount of diesel fuel exits the engine unburned, and these airborne hydrocarbons can combine with other particles in the atmosphere to form larger particles.

The problem of incomplete combustion in diesel engines is exacerbated by the nature of diesel fuel. Diesel fuel is derived from crude oil and is a complex mixture of various petroleum components. This complex composition makes it inherently more challenging to achieve complete combustion, leading to higher levels of unburned fuel released into the atmosphere.

Furthermore, diesel engines tend to have a longer lifespan compared to other types of engines, often operating for 30 years or more. As a result, older, less efficient, and dirtier diesel engines remain in use for extended periods, contributing to higher levels of pollution over time. The durability and efficiency of diesel engines have led to their widespread use, especially in heavy-duty vehicles such as big-rigs and garbage trucks, which further increases their overall environmental impact.

To address the issue of diesel engine pollution, the U.S. Environmental Protection Agency (EPA) has implemented several measures. These include establishing standards for the sulfur content of diesel fuel and emissions standards for new diesel engines. The introduction of Ultra-Low-Sulfur Diesel (ULSD) fuel has significantly reduced sulfur concentrations in diesel fuel, leading to cleaner-burning engines. Additionally, the Diesel Emissions Reduction Act of 2010 provides funding for projects aimed at reducing diesel emissions from existing engines, further contributing to the effort to mitigate the polluting effects of diesel engines.

Internal combustion engines (ICEs) are a significant environmental threat, producing particle emissions that harm all organisms

Internal combustion engines (ICEs) are a significant environmental threat. They produce particle emissions that harm all organisms, including humans. ICEs are heat engines that generate power by consuming fuel via combustion. Most commonly, they consume carbon-based fossil fuels, such as gas or diesel, which emit significant pollutants into the environment.

Over the last 200+ years, measurements of atmospheric carbon dioxide have risen from 278 parts per million (ppm) to over 417 ppm—a 50% increase. This increase in carbon emissions has disrupted nature's lifecycles and systems, impacting all organisms. With enough emissions, the environment's natural processes for sequestering carbon, such as photosynthesis, cannot keep pace. The excess atmospheric carbon traps heat, leading to climate shifts and general temperature increases, which, in turn, influence various other environmental cycles.

The pollution caused by ICEs includes greenhouse gases (GHGs), which contribute to climate change and global warming by absorbing energy. Additionally, hydrocarbon fuels can contaminate soil and water, negatively impacting growth rates, health, and biological processes for all organisms. Increased emissions of particulate matter (PM) and hydrocarbons in the atmosphere have detrimental effects on both the environment and human health. This includes reduced visibility (haze), damage to crops, trees, and other vegetation, and an increased risk of cancer.

Diesel engines, in particular, have been associated with more significant environmental and health risks. They produce more emissions pollution because they do not always burn all the fuel they consume, resulting in "incomplete combustion." This issue is exacerbated when there is a lack of oxygen or insufficient temperature during the combustion process. The leftover fuel, or unburned hydrocarbons, is forced out of the combustion chamber during the four-stroke cycle, contributing to higher levels of atmospheric pollutants.

While technological advancements have reduced the environmental impacts of ICEs, the overall environmental burden of internal combustion engines is still significantly higher than that of electric battery vehicles.

Carbon monoxide is produced by engines with an inadequate fuel-air ratio and is toxic to humans

Carbon monoxide is a highly dangerous, colourless, odourless, and poisonous gas that is produced by the incomplete combustion of carbon-based fuels, such as coal, wood, charcoal, oil, kerosene, propane, and natural gas. Engines that rely on these fuels, including cars, lawn mowers, and portable generators, can produce carbon monoxide when the fuel-to-air ratio is incorrect or when combustion is incomplete.

When an engine burns fuel, the ideal ratio of air to fuel is around 14.7:1. This ratio ensures that the fuel is completely burned, producing carbon dioxide and water vapour. However, if there is not enough oxygen during combustion, the fuel does not burn completely, resulting in the formation of carbon monoxide. This can occur when an engine is poorly maintained, when there is a blockage in the air intake or exhaust system, or when the air-fuel mixture is incorrect, such as when an engine is tuned to increase power.

Carbon monoxide is harmful to humans because it interferes with the body's ability to transport oxygen. When inhaled, carbon monoxide enters the bloodstream and binds to haemoglobin, the protein in red blood cells that carries oxygen. This binding forms carboxyhaemoglobin, which prevents oxygen from being transported throughout the body. As a result, oxygen-dependent tissues and organs, such as the heart and brain, can be deprived of oxygen, leading to serious health issues and even death.

The effects of carbon monoxide poisoning can vary depending on the concentration of the gas, the length of exposure, and individual health factors. Initial symptoms may include headache, weakness, dizziness, nausea, tachycardia (increased heart rate), and tachypnea (rapid breathing). Prolonged exposure to high concentrations of carbon monoxide can lead to disorientation, unconsciousness, and death. Some people may experience cognitive sequelae, or long-term neurological effects, following carbon monoxide poisoning.

To prevent carbon monoxide poisoning, it is important to ensure proper ventilation and avoid operating gasoline-powered engines in enclosed spaces. Carbon monoxide detectors should be installed in homes and regularly maintained to provide early warning of dangerous levels of carbon monoxide.

Nitrogen oxides, produced by high-temperature combustion, combine with other compounds to form particulate matter that is harmful to human health

Nitrogen oxides, or NOx, are a group of highly reactive gases, including nitrogen dioxide (NO2), nitric oxide (NO), nitrous oxide, nitrous acid, and nitric acid. These gases are formed during the combustion of fossil fuels, such as coal, oil, gas, or diesel, at high temperatures. While nitrogen is abundant in the air we breathe, it is typically non-reactive under standard conditions. However, in the presence of high temperatures and oxygen, as in the case of combustion, nitrogen can react with oxygen to form nitrogen oxides.

These nitrogen oxides are released into the atmosphere through vehicle emissions, power plant operations, and off-road equipment. Cars, trucks, and buses are the largest sources of NO2 emissions, followed by non-road diesel-powered equipment and industrial processes. The combustion of fuel in internal combustion engines, as well as the emission of air and fuel residuals from vehicle tailpipes, are significant contributors to the release of nitrogen oxides.

Once emitted, nitrogen oxides, particularly NO2, can react with other chemicals in the atmosphere, such as volatile organic compounds, water, and oxygen. These reactions lead to the formation of secondary pollutants, including particulate matter, ozone, and acid rain. Particulate matter refers to the tiny solid and liquid particles suspended in the air, which can include nitrate particles formed from the reaction of NOx with other compounds.

The presence of particulate matter in the air poses a significant threat to human health. When inhaled, these particles can irritate the airways and damage the human respiratory system. This is especially detrimental to individuals with asthma and those who are more vulnerable, such as children and the elderly. Prolonged exposure to elevated levels of particulate matter can contribute to the development of respiratory issues and potentially increase susceptibility to respiratory infections.

To address the harmful effects of nitrogen oxides and particulate matter, regulatory bodies like the US EPA have established standards and implemented measures to reduce emissions. The Clean Air Act, for instance, has helped drive down nitrogen dioxide emissions, leading to improved air quality nationwide. Additionally, catalytic converters are commonly used in vehicles to reduce toxic gases and pollutants in exhaust gases through redox reactions.

Frequently asked questions