What are the current trends and challenges in the research and development of internal combustion engines?

1 Thermal efficiency

Thermal efficiency is the ratio of the useful work output to the heat input of an engine. It measures how well an engine converts fuel energy into mechanical work. The higher the thermal efficiency, the less fuel consumption and emissions per unit of work. Thermal efficiency depends on several factors, such as the engine cycle, compression ratio, fuel type, air-fuel ratio, combustion temperature and pressure, heat transfer, and friction losses. In general, thermal efficiency increases with higher compression ratios, leaner mixtures, and higher combustion temperatures and pressures. However, these also pose challenges for engine design, durability, and emissions control.

2 Power output

Power output is the rate of doing work by an engine. It is proportional to the torque and rotational speed of the engine. The higher the power output, the faster and stronger the engine can perform. Power output depends on several factors, such as the engine displacement, cylinder configuration, valve timing, fuel injection, turbocharging, and intake and exhaust systems. In general, power output increases with larger displacement, higher cylinder number, advanced valve timing, direct fuel injection, turbocharging, and optimized intake and exhaust systems. However, these also increase the engine complexity, cost, and weight.

3 Engine cycle

The engine cycle is the sequence of processes that occur in one revolution of the crankshaft in an ICE. There are different types of engine cycles, such as the Otto cycle, the Diesel cycle, the Atkinson cycle, and the Miller cycle. Each cycle has different characteristics and advantages for different applications. The Otto cycle is the most common cycle for spark-ignition engines. It consists of four processes: intake, compression, expansion (or power), and exhaust. The Diesel cycle is the most common cycle for compression-ignition engines. It consists of four processes: intake, compression, combustion (or power), and exhaust. The Atkinson cycle and the Miller cycle are variations of the Otto cycle that use different valve timings to achieve higher expansion ratios and lower compression ratios. They aim to improve the thermal efficiency and reduce the pumping losses of the engine.

4 Compression ratio

The compression ratio is the ratio of the maximum volume to the minimum volume of the cylinder in an ICE. It is an important parameter that affects the thermal efficiency, power output, and emissions of the engine. The higher the compression ratio, the higher the pressure and temperature at the end of the compression process, which leads to more efficient combustion and higher work output. However, there are limits to how high the compression ratio can be. For spark-ignition engines, too high compression ratios can cause knock or detonation, which is the uncontrolled ignition of the fuel-air mixture before the spark plug fires. This can damage the engine and reduce the performance. For compression-ignition engines, too high compression ratios can cause excessive heat and pressure, which can increase the emissions of nitrogen oxides (NOx) and particulate matter (PM).

5 Fuel type

The fuel type is another parameter that affects the thermal efficiency, power output, and emissions of ICEs. Different fuels have different chemical compositions, energy densities, octane ratings, cetane numbers, and combustion characteristics. The energy density is the amount of energy per unit mass or volume of fuel. The higher the energy density, the more energy the fuel can provide for a given amount of fuel. The octane rating is a measure of the resistance of a fuel to knock or detonation in spark-ignition engines. The higher the octane rating, the more compression the fuel can withstand without knocking. The cetane number is a measure of the ignition quality of a fuel in compression-ignition engines. The higher the cetane number, the easier the fuel ignites under compression. Common fuels for ICEs include gasoline, diesel, natural gas, ethanol, biodiesel, and hydrogen.

6 Air-fuel ratio

The air-fuel ratio is the ratio of the mass of air to the mass of fuel in the fuel-air mixture that enters the cylinder in an ICE. It is an important parameter that affects the combustion efficiency, power output, and emissions of the engine. The stoichiometric air-fuel ratio is the ideal ratio that ensures complete combustion of the fuel with no excess air or fuel. For gasoline, it is about 14.7:1. For diesel, it is about 14.5:1. However, in practice, engines often operate at different air-fuel ratios depending on the load and speed conditions. Lean mixtures have more air than fuel than the stoichiometric ratio. They can improve the thermal efficiency and reduce the emissions of carbon monoxide (CO) and hydrocarbons (HC), but they can also reduce the power output and increase the emissions of NOx. Rich mixtures have less air than fuel than the stoichiometric ratio. They can increase the power output and reduce the emissions of NOx, but they can also reduce the thermal efficiency and increase the emissions of CO and HC.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?