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This article was first published in 2003.
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Refrigerated intercoolers that are bypassed most of the time, membranes used on the intake system to separate oxygen and nitrogen from the air, and a tuned-length intake system which is simplicity itself - we trawl the US Patents Office looking at new designs of intake systems.
Variable Intercooled Intake
It sounds simple enough but the fact that Brent Sealy of the US could recently patent the idea shows that no-one else has beaten him to it. The invention is a dual-path intake system - one path for non-boosted and intercooled air, and the other for the high pressure and intercooled stuff. Making it a bit more interesting is the refrigeration technique used for the intercooling side of things.
But why the need for the two-path approach?
Brent explains, "The present invention relates to a system for providing chilled and super-atmospheric air charge to an engine on a preferential basis.
"Engine designers have devised a potpourri of systems for increasing the density and decreasing the temperature of the air charge entering an internal combustion engine. For ordinary driving, it is desirable, on only a very infrequent basis, to operate the engine at its highest possible output. Thus, it is not desirable or necessary, from the standpoint of cost, fuel consumption, or weight to have a system which is capable of providing densified [ie boosted] and chilled air to the engine on a continuous basis in a quantity sufficient to support the engine's maximum output."
The new invention overcomes these disadvantages by "providing alternative pathways for air to enter the engine's air supply plenum."
"Thus, during normal operation, the air will enter into the unchilled passageway, allowing the chilling apparatus to be pulled down to a very low temperature so as to provide a transient but very high level of densification and charge cooling.
"Because the densification apparatus does not operate continuously, power consumption of the apparatus is low. Moreover, because chilling is not required to operate continuously, a very high level of chilling is available on an intermittent basis, which is consistent with usage of such system for normal driving."
A splitter valve is used to determine the path that the intake air takes - where it's direct or through the supercharger (or turbo) and intercooler. The intercooler - a water/air design - "may... be chilled by a liquid-to-liquid heat exchanger, which is exposed to a refrigerated fluid."
"Liquid coolant is chilled by the air-to-liquid heat exchanger only if the temperature of the liquid coolant leaving the inner cooler exceeds the ambient air temperature by an amount greater than a predetermined threshold. If the temperature of the liquid coolant leaving the intercooler is less than a predetermined threshold temperature, a heat exchanger bypass valve will be closed so as to allow the liquid coolant to circulate only through the liquid-to-liquid heat exchanger.
"The refrigerated fluid, which chills the liquid coolant in the liquid-to-liquid heat exchanger, comprises refrigerant fluid flowing in a vehicle air conditioning system. The air conditioning system is called upon to furnish the refrigerant fluid only if the demand placed upon the air conditioning system is less than a predetermined threshold. In other words, if the vehicle occupants demand a high level of air conditioning service, refrigerant fluid will not be allowed to flow to the liquid-to-liquid heat exchanger.
"As noted above, the flow of charge air through the first and second ducts is controlled by a splitter valve, which is itself controlled so as to send most of the air into the plenum through the second duct in the event that the throttle associated with the engine is opened at a rate exceeding a threshold opening rate. Similarly, the splitter valve is controlled so as to send most of the air into the plenum through the second duct in the event that the airflow through the engine exceeds a threshold airflow rate."
Oxygen-Enriched Air
An intake system adapted to separate air into its component oxygen and nitrogen parts before feeding it into the engine sounds the stuff of fantasy, but Charles Dutart of the Caterpillar company in the US has just taken out a provisional patent on the idea.
So why the need to adopt this approach?
"In recent years, internal combustion engine makers, and in particular diesel engine manufacturers, have been faced with ever increasing regulatory requirements, namely exhaust emissions regulations. Exhaust emissions takes on a number of forms including visible smoke, particulate matter and oxides of nitrogen (NOx).
"To address these emissions issues, different technologies have been developed or used, including fuel injection and combustion control strategies and systems, after-treatment systems, exhaust gas recirculation (EGR) systems, and, in some cases intake air separation systems.
"Many emission reduction systems have a negative effect on fuel efficiency.... One well-known method of improving engine fuel efficiency or power density is by increasing the amount of oxygen in the cylinder. Typically this has been accomplished by pressurizing the air taken into the combustion chamber. The main goal of this pressurization is to increase the oxygen available for combustion.
"It is well known that the introduction of oxygen-enriched intake air during the intake stroke of facilitates burning a larger part of the available fuel injected which in turn increases the power output for each combustion cycle or charge, and generally reduces brake specific fuel consumption (BSFC). Lower BSFC correlates strongly with reduction in unburned fuel and overall improvement in fuel economy.
"In addition to decreasing BSFC, increasing air intake oxygen content serves to reduce the quantity of unburned hydrocarbons by increasing the likelihood of complete combustion."
So how does the Caterpillar system work?
The major ingredient is an air separation membrane which is "adapted for separating the intake air into a flow of the oxygen enriched air and a flow of nitrogen enriched air".
The patent shows the system fitted to a turbocharged and intercooled in-line diesel engine, but makes the point that such a system would be quite at home on a normal petrol engine. A turbo (green) blows the induction air through an intercooler (light blue). Following that it passes through the air separation device (purple). This device includes two inlets and two outlets.
The first inlet (light green) receives the air to be separated into an oxygen-rich stream and a nitrogen-rich stream. The second inlet (yellow) receives a flow of sweep air or purge air which enhances the effectiveness of the air separation device. The first outlet (orange) receives the flow of oxygen enriched air combined with purge air. The second outlet (red) is for the nitrogen-enriched air. The variable valve on the oxygen-enriched outlet (dark blue) varies the amount of oxygen -nriched air that flows through it and by doing so, controls the relative concentrations of nitrogen and oxygen in the air directed to the intake manifold.
"Selective operation of this valve allows the engine to operate in essentially three different charge air modes, namely nitrogen enriched mode (i.e. valve partially or fully open), standard intake air mode (i.e. valve closed for selected length of time), and transient oxygen enriched mode, which occurs for a short period or duration as the valve is first closed."
An ECU (black) controls the operation of this valve, in addition to other normal engine management functions.
So what on earth does the air separation membrane device look like? A large number of selectively permeable membrane elements or fibres are placed in a spiral orientation. These are "hollow, porous, coated tubes through which selected gases such as hydrogen, helium, water vapours, carbon dioxide, and oxygen tend to permeate outwardly through the membrane at a relatively fast rate while other gases, such as carbon monoxide, argon and nitrogen permeate less rapidly and are mostly retained and transported along the membrane tubes.
"Different gases present in the intake or feed air tend to permeate through the membrane at different relative permeation rates and generally through the side walls of the membrane. The rate of permeation is also dependent, in part, on the membrane temperature, and therefore, altering or controlling the temperatures of gases entering the air separation device ultimately controls permeability.
"The intake air is introduced into the intake air separation housing and air separation membrane in a... direction that is generally along the length of the membranes. In this manner the intake air is transported or flows generally along the length of the air separation unit and thereby exposed to greater surface area of the membrane, which tends to enhance the air separation effects.
"Conversely, the flow of purge air is introduced into the air separation housing and air separation membrane in a cross flow direction such that the purge air flows generally across the outer surfaces of the membrane. This cross-flow orientation operates to enhance the effectiveness of permeation or air separation that is occurring to the intake air."
So in this system what happens to the oxygen enriched air? It appears that it is fed either to the atmosphere or the exhaust. However, "in certain high load and/or transient load conditions, the oxygen demand of the engine may warrant recombining some or all of the permeate flow with the... nitrogen enriched air flow".
So the main purpose of this design is to drop emissions by introducing more nitrogen into the combustion process, with the bonus that on transients the oxygen supply to the engine can be boosted. However, there appears to be nothing to stop the system being used to increase oxygen concentrations of the intake air, with the nitrogen-enriched air rather than the oxygen-enriched air being the gas to be dispensed with...
Ford's Tuned Intake
All engines run tuned intake systems, where pressure waves run up and down inside the runners. The trick is to get a high pressure wave arriving back at the inlet valve at just the time it is again opening - so increasing the amount of gas that flows into the combustion chamber. This tuning can be achieved in all sorts of ways, as the variety of intake manifold designs shows. However, Thomas Ma - of the Ford Motor Company - has invented a new system of tuning intakes which is also very simple.
So why the need for a new system?
"Conventionally the intake tracts of a multi-cylinder engine are brought together to a common plenum chamber, each tract opening into the plenum chamber at a point which is designed to experience the minimum flow interference from the other tracts. The tracts function as tuned lengths for which there is one engine speed where the torque is enhanced because of resonance of the pressure wave excitations within the intake system.
"More specifically, when the inlet valve starts to open, at the beginning of a four stroke cycle, the combustion chamber is still under pressure from the exhaust stroke of the previous cycle and a pressure wave passes out of the intake port and propagates at the speed of sound along the intake tract. This wave travels the entire length of the intake tract until it reaches the plenum chamber at which point it is reflected with opposite phase. A further three traverses of the entire length of the intake tract and two reflections at the open and closed ends of the tract are necessary before the wave again reaches the intake port as a positive pressure wave.
"Thus, with a fixed length tract, there are engine speeds at which the reflected pressure wave increases the charge density at the instant when the inlet valve closes so as to improve volumetric efficiency but other speeds when the wave arrives as a negative pressure tending to reduce volumetric efficiency.
"To obtain an improvement at low engine speeds, a long tract length is required but this has the disadvantage of increasing the package size and the resistance to flow at high engine speeds.
"The invention therefore seeks to provide a longer tuned length without increasing the size of the intake system and to avoid performance degradation from reflected waves having a negative pressure."
It does this by a very simple technique: the openings to the intake runners of cylinder pairs where the valve events don't overlap are arranged so as to face one another inside the plenum. The mouths are separated by a gap "which is narrower than the diameter of the tracts, the gap being sufficiently wide to permit mass air flow between the respective tracts and the common passage but being sufficiently narrow to couple most of any pressure wave energy emanating from one tract directly into the other tract."
"Preferably, the gap between the ends of the tracts within the plenum chamber should be between one quarter and one half of the diameter of the tracts.
"This arrangement permits mass air flow to enter freely into either one of the intake tracts yet at the same time a pressure wave coming from either tract is transmitted across to the opposite tract which now functions as a resonance column with a closed end. By ensuring good coupling of the pressure wave across the facing pipes, the effective tuned length is made equal to the combined length of the two tracts and the pressure wave can propagate several times along its length with closed-end reflections at both ends. Because both ends of the resonating column are closed, the pressure wave suffers no pressure inversion as would be the case in a conventional tract.
"Because no reflection is inverted, there are twice as many engine speeds at which the resonance tuning is effective and the engine will experience torque enhancement at low speed as well as at high speed. This is achieved with no increase in size relative to a conventional intake system and no need of a variable geometric system. There is also no increase in friction as the tract carrying the flow is short."
Conclusion
While these ideas are patented, there's little stopping individual enthusiasts from adopting some of the ideas in their modifications...
