2023-06-01 22:00:00
When charge air coolers were introduced in the 1990s, the heat exchanger was sized as a simple component simply defined by its thermal power and its pressure drop, a function of the intake air flow and the air speed in front of the vehicle.
The latest engine improvements in terms of fuel reduction and compliance with increasingly stringent anti-pollution standards have led to an increase in the need for charge gas cooling. The introduction of the WLTC harmonized cycle (Worldwide harmonized Light vehicles Test Cycle), then the RDE cycle (Real Driving Emissions), will accentuate this trend by the need to increase the rate of use of recycled gases (or external dilution more commonly referred to by the acronym EGR for Exhaust Gas Recirculation) on more heavily loaded engine points.
CO neutral mobility2 is the key phrase of the contemporary automotive industry. Going from carbon mobility to neutral mobility cannot be done in the very short term; this is the reason why manufacturers and equipment manufacturers are still working on improving internal combustion engines in order to reduce their carbon impact. In the future, the CO2 and more generally greenhouse gases will have to be assessed taking into account the global life cycle from cradle to grave. But for the moment, only the CO2 coming from the exhaust pipe is taken into account. This is the reason why the energy efficiency of the Internal Combustion Engine (ICE) must be improved once more when it is still needed, or simply shut down when another device has the capacity to ensure the propulsion alone. This is the golden rule for future hybrid powertrains.
Diesel engines, which are still very competitive on this subject, are now technically ready to comply with future emissions regulations; SCR technologies, Water Charge Air cooling(WCAC) coupled to low and high pressure EGR are now widely available on the market and play a full part in overcoming the weaknesses of Diesel. Be that as it may, the current debate around the restrictions on the use of this type of engine has forced manufacturers and equipment manufacturers to work on the gasoline engine, in order to reinforce the potential of spark ignition MCI technology, but also to document the possibility of using alternative fuels (ethanol, gas, synthetic fuels “e-fuel”, hydrogen).
The tendency to Downsizing and at Downspeeding clearly constrains engine manufacturers to better integrate the downstream compressor gas cooling function for which new requirements and functionalities are being felt, such as:
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a significant reduction in the pressure drop in order to increase the pressure upstream of the intake valves: this is equivalent to an increase in the boost pressure;
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a reduction in the volume of air downstream of the compressor in order to reduce response times (time to torque) and reduce the number of engine cycles required to drain the air line (better control of the dilution rate in transients);
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stability of the temperature downstream of the exchanger: it must be less dependent on driving conditions (vehicle speed) and the pollution control strategy (high, low pressure or combined EGR rate);
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the possibility of controlling the temperature downstream of the exchanger according to the engine operating points, the depollution strategy (problem of condensation in low pressure EGR, regeneration of the particulate filter) or engine life (improvement of cold starts, reduction of time to light off catalyst);
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an increase in thermal performance and the limitation of parasitic heating downstream of the exchanger;
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the addition of active functionality (throttle body, air metering, EGR module, Swirl flap, cylinder deactivation, etc.);
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compatibility with all the vehicle platforms of the manufacturer(s).
This need to integrate the charge gas cooling function requires studying all the components, from the compressor outlet to the intake valves, such as a multi-component system called the “intake module” or “air line overfeeding”.
This article will deal with the modeling of the components of the intake air line, the different known architectures and will present the main ways of improving current architectures.
At the end of the article, the reader will find a glossary and a table of acronyms, notations and symbols used.
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