Intake Air Management for Diesel Engines

Hannu Jääskeläinen, Magdi K. Khair

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Abstract: Managing the supply of air to the combustion chamber is an important process to ensure consistent and reliable performance of modern diesel engines. Air management encompasses all aspects that affect the quantity, composition, temperature, pressure, bulk motion and cleanliness of the combustion air at the start of the heat release period. Details of the intake system, cylinder head and valve train design, pressure boosting technology and charge dilution requirements are all important aspects of intake air management.

Introduction

Managing the supply of air to the combustion chamber is a critical aspect of modern diesel engines and can impact emissions, performance and fuel economy. Combustion air management is the process that is used to ensure that the air supplied to the combustion chamber at all operating conditions meets a number of requirements including:

In older engine designs that did not have to meet stringent exhaust emissions requirements, air management systems could be relatively straightforward. In some cases, it was sufficient to simply ensure that the air was clean, that the flow capacity of the intake system was adequate to ensure peak torque and power objectives were met and sufficient swirl was imparted to the air as it entered the combustion chamber to support the fuel injection system in the task of mixing of air and fuel. Typically, no active control of any intake side hardware was required. Even as many engines started to adopt turbochargers and other forms of intake air compression, it was sufficient to simply ensure a proper match between the engine and compressor.

Pressure to lower emissions while maintaining or improving other engine performance parameters required that the intake air properties be better controlled and matched to suit the engine operating condition. This required the introduction more hardware to control these intake air properties. For example, wastegate control on the turbocharger was introduced to enable improved intake air boosting at lower engine speeds and to limit turbine speeds at high engine speeds, valves were introduced to mix some exhaust gas (EGR) into the intake air at some engine operating conditions, turbocharger controls become more complicated to ensure that boost and EGR requirements could be met and higher and higher intake air pressures required that the higher intake air temperatures resulting from compression be limited. All of this added complexity required that more sophisticated control systems with sensors and sophisticated control algorithms be incorporated to ensure everything functions as expected.

This paper covers the basics of pressure charging—including turbochargers, superchargers and systems with multiple compressors—as well as turbocompounding and an introduction to intake manifold design. There are a number of additional important aspects of intake air management that will be discussed in separate papers. These include:

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