Greta Jimenez
Diesel engines have been criticised for their emissions, but the technology has improved over time. While diesel engines emit less CO2 and greenhouse gases than petrol engines, they require large amounts of air for fuel combustion, which releases more air pollutants, including nitrogen oxides and fine particles. On the other hand, petrol engines are becoming more polluting as they develop, with the direct injection system increasing fine particle emissions. So, while diesel engines were initially considered more polluting, new well-maintained diesel cars built to the latest standards now have similar emissions to new petrol vehicles.
Diesel vs Petrol Engines: Which is More Polluting?
| Characteristics | Values |
|---|---|
| CO2 Emissions | Diesel engines emit less CO2 than petrol engines. |
| Greenhouse Gas Emissions | Diesel engines emit fewer greenhouse gases. |
| Fuel Efficiency | Diesel engines use less fuel to achieve the same performance as petrol engines. |
| Fuel Composition | Diesel fuel contains slightly more carbon than petrol. |
| Air Pollutants | Diesel engines require more air for fuel combustion, leading to increased chemical reactions and air pollutants, including nitrogen oxides and fine particles. |
| Particulate Filters | Diesel engines use particulate filters to reduce mass-particle emissions, but these filters can clog in urban driving conditions. |
| Health Impact | Fine particulate matter emitted from diesel engines is associated with poor heart health and increased hospital admissions. |
| Government Regulations | Some governments plan to discourage or ban diesel vehicles in urban areas due to their toxic emissions. |
| Maintenance | Petrol emissions systems are self-regulating and require less owner input than diesel engines, which may need regular additions of a urea mixture. |
| Technology Improvements | New, well-maintained diesel cars built to the latest standards have similar emissions to new petrol vehicles. |
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What You'll Learn
Diesel engines emit more harmful pollutants
Diesel engines have been criticised for the high levels of harmful emissions they produce. While diesel engines emit less CO2 and greenhouse gases than petrol engines, they emit more toxic air pollutants. These include nitrogen oxides, ground-level ozone, and fine particles such as polycyclic aromatic hydrocarbons, PM10, PM2.5, NO2, and NOx.
The additional air required for fuel combustion in diesel engines causes more chemical reactions, which in turn release more air pollutants. The increased production of fine particles is associated with poor heart health. Research has shown that higher concentrations of particulate matter in the air lead to more hospital admissions and deaths from heart attacks.
To address the issue of toxic emissions from diesel engines, manufacturers have introduced particulate filters. These filters can remove up to 99% of diesel polluting mass particles. However, they tend to clog in urban driving conditions and require the regular addition of a urea mixture. In contrast, petrol emissions systems are self-regulating and require less maintenance.
While new, well-maintained diesel cars built to the latest standards have similar emissions to new petrol vehicles, the overall impact of diesel engines on pollution is still a complex issue. The fast-evolving nature of engine technology and the focus on specific aspects of emissions, such as CO2 output, can obscure the full picture of the environmental impact of different fuel types.
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Diesel engines require more driver maintenance
Diesel engines have been criticised for the amount of toxic emissions they produce, with some governments even planning to ban them from urban areas. However, diesel engines emit less CO2 and greenhouse gases than petrol engines. This is because diesel engines have a higher compression ratio and perform better than petrol engines, meaning less fuel is used to travel the same distance.
Despite this, diesel engines do require more driver maintenance than petrol engines. Firstly, diesel engines require more frequent replacement of fuel filters. This is because diesel fuel is denser and more refined than petrol, meaning it can attract and contain more contaminants that can damage the fuel injectors and other components if not filtered properly. Secondly, diesel engines require ample air intake for optimal function, so their air cleaners might need more frequent servicing to prevent debris from hindering performance. Thirdly, diesel engines generate more heat than petrol engines, so the cooling system must work harder and requires more frequent maintenance to prevent overheating and corrosion. This includes regularly checking coolant levels, inspecting hoses, and ensuring the radiator is clean.
Furthermore, diesel engines produce more soot, which can contaminate the oil, so it is essential to use the correct grade of oil and change it more frequently. Diesel engines are also typically equipped with turbochargers, which require special care and proper lubrication to prevent failure. Finally, diesel engines use glow plugs, which are especially important in colder climates to preheat the combustion chamber and ensure a smooth engine start. While glow plugs do not need to be replaced as often as spark plugs in petrol engines, they should be checked regularly.
While diesel engines may require more maintenance, they tend to last longer due to their forged internals. Additionally, some diesel engines, like the I-6 Cummins, are known for their simplicity and easy maintenance. Ultimately, the decision between a diesel or petrol engine comes down to personal preference and intended use.
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Petrol engines are catching up to diesel in terms of fine particle emissions
The diesel engine has long been associated with high levels of emissions, particularly fine particulate matter. However, this narrative is evolving as manufacturers have made significant strides in reducing diesel emissions over the last three decades. The introduction of particulate filters, for instance, has led to a 90-99% reduction in diesel polluting mass particles.
While diesel engines have cleaned up their act, petrol engines are catching up in terms of fine particle emissions. The recent introduction of a direct injection system in petrol engines, which sprays fuel into the cylinder at high pressure to reduce fuel consumption, has significantly increased the number of fine particulate pollutants. As a result, the fine particle emission rates of petrol engines are rising and could eventually match those of diesel engines.
This shift in petrol engine emissions has important health implications. Fine particulate matter emitted from diesel engines has been linked to poor heart health, with research showing that increases in background concentrations of particulate matter lead to more hospital admissions and deaths from heart attacks. With petrol engines emitting more fine particles, similar health concerns could arise.
It is worth noting that the discussion of engine emissions is complex and ever-evolving. The technologies and standards for diesel and petrol engines are constantly improving, and the focus on one type of pollution, such as CO2 output, can cause other types, like toxic emissions, to be overlooked. Additionally, the performance of engines can vary depending on factors like model, age, and usage.
In conclusion, while diesel engines have historically been associated with higher emissions, particularly fine particulate matter, the latest well-maintained diesel cars built to modern standards now have similar emissions levels to new petrol vehicles. At the same time, the increasing fine particle emission rates of petrol engines due to technological developments mean they are catching up to diesel engines in this regard.
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Diesel engines are lean-burn
Diesel engines are "lean-burn", meaning they use less fuel and more air to achieve the same performance as a petrol engine. This results in lower fuel consumption and carbon dioxide emissions than current engines operating at a stoichiometric air-to-fuel ratio. However, the presence of oxygen in their emissions prevents the use of current "three-way" type catalysts, and the additional air causes more chemical reactions, releasing air pollutants such as nitrogen oxides and fine particles.
Lean-burn engines admit twice as much air as is theoretically needed for complete combustion into the combustion chambers. The extremely weak air-fuel mixture leads to lower combustion temperatures and, therefore, lower nitrogen oxide formation. While lean-burn gas engines offer higher theoretical thermal efficiency, transient response, and performance may be compromised in certain situations.
Diesel engines are considered to be lean-burning with respect to total volume. However, the fuel and air are not well mixed before combustion. Ignition occurs in the initial stages of the breakdown of separate layers while substantial amounts of each layer still exist. Because the spark plug is located closer to the vortex consisting of the air-fuel mixture, ignition arises in an area of the pentroof-design combustion chamber where fuel density is higher. The flame then spreads through the combustion chamber via small turbulences. This provides stable combustion even at normal ignition energy levels, thereby realising lean-burn.
The engine computer stores optimum air-fuel ratios for all engine-operating conditions, from lean (for normal operation) to the richest (for heavy acceleration) and all points in between. Full-range oxygen sensors provide essential information that allows the computers to properly regulate fuel delivery.
One of the newest lean-burn technologies available in automobiles currently in production uses very precise control of fuel injection, a strong air-fuel swirl created in the combustion chamber, a new linear air-fuel sensor (LAF type O2 sensor), and a lean-burn NOx catalyst to further reduce the resulting NOx emissions that increase under "lean-burn" conditions and meet NOx emissions requirements.
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Diesel engines require large amounts of air for fuel combustion
Diesel engines are unique in that they require large amounts of air for fuel combustion. Unlike petrol engines, which take a pre-mixed mixture of air and fuel, diesel engines compress air and then inject the fuel into the compressed air. This compression of air, which occurs at a ratio of 14:1 to as high as 25:1, raises the air temperature, and the heat of the compressed air ignites the fuel spontaneously.
The high compression ratio of the diesel engine leads to better efficiency. This is because the higher the compression ratio, the more power generated. As a result, diesel engines use less fuel to travel the same distance as petrol engines, leading to lower carbon dioxide (CO2) emissions.
However, the additional air required by diesel engines for fuel combustion causes more chemical reactions, which release significant amounts of air pollutants. Among these pollutants are dioxides and nitrogen oxides, gases and fine particles, such as polycyclic aromatic hydrocarbons, ethane, and ethylene. These fine particles have been associated with poor heart health, leading to more hospital admissions and deaths from heart attacks.
While new, well-maintained diesel cars built to the latest standards have similar emissions to new petrol vehicles, the technology used in diesel engines has been criticised for its emissions. Manufacturers have installed particulate filters to meet new, more restrictive standards on diesel particulate matter pollution, and these filters can remove between 90 and 99% of diesel polluting mass particles. However, these filters cannot retain the finest particles, which are also the largest ones, and there is conflicting evidence about the effectiveness of these filters in reducing NOx emissions.
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Frequently asked questions
Yes, diesel engines are more polluting than petrol engines. Diesel engines emit more harmful pollutants, such as ground-level ozone and particulate matter, which is associated with poor heart health.
Diesel engines emit a variety of harmful pollutants, including dioxides, nitrogen oxides, polycyclic aromatic hydrocarbons, ethane, and ethylene.
Diesel engines require large amounts of air for fuel combustion, which leads to more chemical reactions and the release of more air pollutants.
Yes, the fine particulate matter emitted by diesel engines has been linked to poor heart health and increased hospital admissions for heart attacks.
Manufacturers have installed particulate filters, which can remove up to 99% of diesel polluting mass particles. Additionally, fuel standards, such as the EPA's Ultra-Low-Sulfur Diesel (ULSD) fuel, aim to reduce the sulfur content of diesel fuels, resulting in cleaner-burning diesel fuel.
