Internal Combustion Engines: internal solutions for a greener future.

Until quite recently, internal combustion engines were predicted to be in a rapid decline due to an increasing trend in e-mobility driven by environmental and performance aspects. However, currently manufacturers place great emphasis on the development of internal combustion engines which future largely depends on their low-emission design. The exhaust gas cleaning methods can be divided into internal and non-engine – exhaust after-treatment systems. In this article, we take a closer look at the former.

From this article, you will learn:

• emission challenges of ICEs.
• the role of emission standards.
• impact of exhaust gases.
• internal solutions for reducing emissions.

Do we have emission issues?

The progressive development of the automotive industry in the second half of the 20^th century led to the appearance of a significant number of motor vehicles powered by an internal combustion engine. Especially in the 1950s and 1960s, the United States faced a problem of excessive environmental pollution. Underpowered power units with imperfect combustion processes turned out to be insufficient over time, so methods were sought to improve the operating parameters of the engines and reduce high specific fuel consumption. The increasing activities of people interested in ecology have drawn attention to the possible depletion of natural fossil fuel resources, environmental pollution and the threat to human health and life due to exhaust gases pollution. As a consequence quantitative and qualitative restrictions on exhaust gas emissions began to appear. The introduction of these limits was preceded by considerations on the complex mechanisms of the formation of harmful and toxic compounds in the combustion engine. It is currently recognized that the fear of destruction of the natural environment caused by exhaust emissions is much greater than the possibility of exhaustion of natural fuel sources as a very large part of the deposits is still undiscovered.

Standards – show stoppers or innovation drivers?

The United States was a forerunner in creating exhaust emission standards by establishing CARB (California Air Resources Board, 1967) and EPA (United States Environmental Protection Agency, 1970), while in the following years Europe, Japan and Australia created their own centers to fight emissions on local markets. As a result, combustion engines are subjected to more and more stringent requirements regarding the emission of harmful and toxic chemical compounds generated during the fuel-burning process.

The emission standards act not only on passenger vehicles but also on the great range of engine-powered heavy-duty vehicles and machinery on the land, boats and ships on the sea and even airplanes that cross the sky – everything that uses the combustion engine. On one hand, it forces engineers to focus on techniques and technologies that reduce exhaust emissions strongly driving innovative approaches, but on the other hand, it controls the development of engines as designers have top-down limitations in mind throughout the entire process of designing the engine and subsystems. What is interesting, the emission standards nowadays relate not only to exhaust gases but may include all factors contributing to pollution such as particulates from tires and brakes. It is also important that excessive emission limits may set conditions that can only be met in a way to promote alternative methods of propulsion such as electrification. E-powered units show their great advantages in a variety of applications proven reliable and efficient over the years, although the complete turn away from combustion technology considering various applications and global perspectives seems not realistic at the moment. In parallel sustainable energy solutions including future fuels for combustion engines have a great chance to succeed. These fuels are designed to offer lower environmental impact compared to conventional fossil fuels like gasoline and diesel.

What is in the pipe?

The idea of ​​using an internal combustion engine is to convert the chemical energy contained in the fuel into mechanical energy. This process is multi-stage and involves the repetition of physicochemical processes. The end result of torque and power is possible thanks to the main chemical process – the combustion reaction between hydrocarbons (HC) from fuel in the presence of air containing oxygen (O₂) and nitrogen (N₂). Exhaust gases considered waste substances form during oxidation and incomplete combustion of petroleum fuels and need to be removed from the engine or reused. The exact composition of exhaust gases depends strongly on the type of fuel, engine design and operating conditions. Although most of the exhaust gases composition belong to pure nitrogen and oxygen, there are three main groups of chemical compounds inside:

• Neutral – H₂O (water vapor)
• Harmful -CO₂ (carbon dioxide)
• Toxic – CO (carbon monoxide), HC (hydrocarbons), NO_x (nitrogen oxides), PM (particulate matter)

For ecological aspects, the most important are toxic compounds that have the most unfavorable impact on the environment and health, which is why the greatest emphasis is placed on combating them. Their total presence can be lower than 1% of the total exhaust gas composition. The processes of formation of toxic compounds are complicated and depend on a number of factors that are characteristic of each compound individually.

Can we clean before we burn?

In the case of currently produced combustion engines, the emission of toxic compounds must be taken into account already at one of the first stages of the design. The design of individual engine components and their functional relations between subsystems have a very important impact on the overall emissions. Appropriate calculations and simulations make it possible to assess whether the structure will be able to meet legally required standards already in the initial design phase. Measures aimed at improving the engine basis, taking into account the reduction of pollutants present in the exhaust gases leaving the engine, are called internal (primary) which mainly include:

• Use of exhaust gas recirculation system – EGR is used mainly to reduce emissions of nitrogen oxides and, indirectly, hydrocarbons. It directs a certain amount of exhaust gases to the cylinder (inlet manifold) so that they can take part in the combustion reaction again. This leads to the partial replacement of oxygen with exhaust gases, which reduces the average temperature of the entire combustion process. Lower cylinder temperature reduces NOx emissions. The positive effect of EGR on hydrocarbon emissions results from the possibility of oxidizing hydrocarbon chains that were only partially broken during the primary combustion process.
• Development of fuel injection systems – precise control of the amount of fuel and the moment of delivery to the cylinder leads to reduced emissions of toxic compounds. High injection pressures allow better mixing of fuel with air in the cylinder breaking large fuel drops into smaller ones and faster evaporation of hydrocarbons. This has a positive effect on particulate emissions, while the amount of nitrogen oxides produced increases. Improved injector design ensures much faster opening and closing times which more precisely control the amount of fuel supplied to the cylinder. Additionally, the injection spray development provides better fuel distribution in the combustion chamber which has a positive effect on the size of fuel drops.
• Improvement of turbocharger efficiency – together with the fuel, an appropriate amount of fresh air must be supplied to the engine for proper combustion. For this purpose, air supply systems equipped with a turbocharger are used, which forces air with increased pressure into the cylinders. Air charging pressure allows you to lower the compression ratio and reduce fuel consumption which results in reduced emissions of toxic compounds while not deteriorating the engine operating parameters.
• Reducing hydrocarbon emissions – a significant problem in the case of combustion engines is the loss of hydrocarbons coming from fuel not actively participating in the combustion process and lubricating oil. There are several sources of clean hydrocarbons from which emissions are limited – the crankcase and the fuel system. During the operation of an internal combustion engine, gas pressure is created in the crankcase, which must be able to escape into the atmosphere to protect the engine against damage. Due to the high temperature of the engine, the lubricating oil evaporates and fuel enters the crankcase as a result of leaks in the cylinder-rings-piston relationship. Modern engines use Closed Crankcase Ventilation (CCV) where the polluted gases and vapors are filtered – oil is returned to the crankcase while gases are reintroduced to the intake manifold.
• Valve timing optimization – development valve timing ensures that the air-fuel mixture is efficiently burned in the combustion chamber. This reduces the amount of unburned fuel and hydrocarbons in the exhaust.

Other methods within the engine can also be distinguished which additionally affect the low emission of toxic compounds in exhaust gases. For example, the optimization of engine cooling systems is used to maintain the temperature of the drive unit in the range of the lowest emissions, electrification of components to reduce the effort of the drive unit or selection of the appropriate quality fuels and oils. Engine designers are actively developing further aspects of combustion engines in order to ensure appropriate quality of exhaust gases.

Keeping ICEs relevant in a greener future

While internal combustion engines face increasing regulatory pressures and competition from electric powertrains, ongoing innovations in emission reduction highlight their continued viability in a transitioning market. Through advanced design strategies, engineers are actively reducing the environmental impact of ICEs. These developments, combined with the exhaust aftertreatment system that we will present in the next article and emerging sustainable fuel options, suggest that ICE technology may still have a meaningful role alongside electric solutions, especially in applications where full electrification remains challenging. As the industry pushes forward, the focus on cleaner combustion technology underscores a balanced approach to mobility that integrates both traditional and alternative propulsion systems, aiming for a sustainable future that leverages the strengths of each.

Jakub Szylar

Project Leader, Powertrain Systems

I have always been passionate about automotive. Some say I must have been born in the garage, but it was my father, a car mechanic, who introduced me to the world of automobiles. As a Project Leader at Endego I feel creative and responsible for work results that bring satisfaction to our clients. Performing both design and management activities I can be a part of any team on the way to success.