Since their inception, diesel engines have dominated the heavy duty trucking sector. The enduring popularity of these engines stems from their longevity, extra torque, towing capability and ease of maintenance. However, the climate crisis and calls for zero-emission vehicles have led many manufacturers to abandon this technology. In spite of these challenges, the diesel engine will still be used in automobiles for the foreseeable future. In order to survive the transition to low and zero-emissions, diesel engines need to be optimized for efficiency and emissions reduction.
This will be achieved by using advanced technologies such as engine control, thermal management and exhaust aftertreatment systems. Some of the most important advancements in diesel engines have been in the area of combustion and emissions control. The development of lean-burn engines and the use of controlled ignition timing (CIT) have reduced combustion temperatures and lowered NOx levels. In addition, new piston designs, use of high compression ratios and improved engine control have also been important in achieving these results. The latest diesel engines have incorporated the concept of cooled exhaust gas recirculation to further reduce NOx emissions and improve fuel economy. This system works by cooling the hot exhaust gases, which cools them and then recirculates them into the combustion chamber at lower temperatures.
This reduces NOx production and increases fuel efficiency by around seven per cent. Another significant advancement has been the introduction of common rail direct injection technology (CRDI). This consists of a single line that supplies fuel to several diesel injectors at a constant pressure. The electronic control unit regulates the amount of fuel injected and this helps to maintain an even combustion. This has resulted in a significant increase in engine performance and fuel efficiency. More recently, a number of automotive companies have reported development of opposed piston diesel engines that may offer further improvements in fuel efficiency and emissions. These engines have fewer moving parts than conventional inline engines and this reduces manufacturing costs as well as weight.
In addition, they can achieve lower cylinder head temperatures, which leads to improved engine combustion and better efficiency. These innovations have resulted in real driving emissions (RDE) test results that have shown diesel engines can meet the EU’s Euro 6d requirements without the need for NOx aftertreatment. However, these results are not yet production ready and more work needs to be done to optimize air, fuel and combustion management as well as develop more effective thermal management strategies.