1、_SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising theref
2、rom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions.Copyright 2011 SAE International All rights reserved. No part of this pub
3、lication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970
4、(outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J2914_201111SURFACEVEHICLEINFORMATIONREPORTJ2914 NOV2011 Issued 2011-11Exhaust Gas R
5、ecirculation (EGR) Cooler Nomenclature and Application RATIONALEThis Information Report defines common terms used to describe the features and application of Exhaust Gas Recirculation (EGR) coolers. 1. SCOPE This document provides an overview on how and why EGR coolers are utilized, defines commonly
6、 used nomenclature, discusses design issues and trade-offs, and identifies common failure modes. The reintroduction of exhaust gas into the combustion chamber is just one component of the emission control strategy for internal combustion (IC) engines, both diesel and gasoline, and is useful in reduc
7、ing exhaust port emission of Nitrogen Oxides (NOx). Other means of reducing NOx exhaust port emissions are briefly mentioned, but beyond the scope of this document. 2. REFERENCES 2.1 Related Publications The following publications are provided for information purposes only and are not a required par
8、t of this SAE Technical Report.2.1.1 Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org.SAE J922 Turbocharger Nomenclature and Terminology SAE J1726 Charge Air Cooler I
9、nternal Cleanliness, Leakage, and Nomenclature SAE J1994 Laboratory Testing of Vehicle and Industrial Heat Exchangers for Heat Transfer and Pressure Drop PerformanceProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 2 of 16
10、 EXHAUSTSTACKEGR COOLERCHARGE AIR COOLERPRE-COOLERAIRFILTEREXHAUSTFILTERINTAKEAIRTURBOJWPUMPEGR FLOWCONTROLVALVEOTHER AFTER TREATMENT3. EXHAUST GAS RECIRCULATION (EGR) COOLER NOMENCLATURE 3.1 EGR in internal combustion engines EGR is a combustion strategy of adding exhaust gas to the intake charge a
11、ir, cooling the mixture to achieve a desired inlet manifold temperature (IMT) of charge air to the cylinder, thereby increasing the specific heat of the charge air mixture entering the cylinder. As a result, for a given fuel energy released by the burned fuel, the peak combustion gas temperature in
12、the cylinder is reduced with the desired effect of reducing NOx output. The higher the percentage mass of EGR, the lower the peak combustion gas temperature, and the lower the NOx produced. Since the heat removed from the EGR flow is transferred into the engine coolant, the downside is a correspondi
13、ng increase in jacket water (JW) heat rejection and required external cooling system capacity. 3.1.1 IMPLICATIONS ON ENGINE DESIGN The addition of EGR into combustion intake flow requires a larger pressure differential across the cylinder to force that mass flow. This differential isnt significant i
14、n engine air system design in IC engines at lower power density or brake mean effective pressure (BMEP). But higher BMEP ratings, especially heavy duty (HD) diesels with turbochargers, higher pressure ratio turbo charging is required than without EGR flow. Increased EGR heat rejection often requires
15、 an increase in JW pump capacity to maintain the same desired T across the radiator at design point heat load. All the following applications of EGR coolers are illustrated with turbocharged EGR air system architectures, and are shown with air to air after-cooling (ATAAC) in the external cooling sys
16、tem. Only the charge air cooling (CAC) related system components are shown. For simplified illustration, other heat exchangers in the coolant circuits (JW or low temperature circuits) are not shown, nor are components of the external cooling system (fans, radiators, etc.). 3.2 EGR System Architectur
17、e Types 3.2.1 Low Pressure Loop EGR FIGURE 1 - LOW PRESSURE LOOP EGR SCHEMATIC Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 3 of 16 Low pressure loop (LPL) EGR is differentiated by its source of exhaust gas taken from
18、 the downstream low pressure side of the turbocharger. Less thermal energy removal (cooling system heat load) is required to reach the desired IMT, since the exhaust gas has already lost some energy after exiting the turbine. Although not required, the gas may also be drawn downstream of the exhaust
19、 particulate filter (as shown in Figure 1), resulting in less particulate matter entering the cylinder before combustion. Both have the added benefit of even lower temperature exhaust to be cooled. The pre-cooler shown in both the LPL and high pressure loop (HPL) figures is optional, and only used i
20、f high enough pressure ratio turbo charging requires cooling of the charge air ahead of the ATAAC to stay below material temperature fatigue limits of the ATAAC core. Advantages over other Architecture1. The biggest advantage of LPL EGR after the exhaust filter (particulate matter (PM) trap), is tha
21、t cleaned exhaust ends up in the cylinder for combustion, with reduced vulnerability to piston, ring, and liner wear related to abrasive exhaust particles. 2. The risk of abrasive wear on the thin walled tubes of the EGR cooler and fouling of the wall surface are also reduced. If the exhaust gas is
22、taken upstream of the PM trap then these two advantages disappear. 3. Because the exhaust gas enters the EGR cooler at a temperature lower than the following high pressure loop (HPL) configuration, the risk of boiling failure modes is decreased. Sufficient JW flow entering the cooler is still requir
23、ed to prevent boiling on the tubes and tube-header joints at the inlet, but to a lesser degree. Thermal cycle fatigue is still a major issue, and not considered a major reduction in risk with LPL architecture. 4. Turbo charger speed and efficiency is less affected by EGR rate than the HPL configurat
24、ion. 5. Mixing of fresh air and EGR flow is very complete. Disadvantages over other Architecture1. The biggest disadvantage of LPL configuration is that corrosive exhaust gas is contained in the ATAAC flow. In designs where the required IMT allows operating conditions where the ATAAC temperature fal
25、ls below dew point, condensation occurs within the core at an acidic level. This drives more expensive material choices or coatings in the ATAAC design. When the charge air is cooled below the dew point, the condensation liquid must also be eliminated before it enters the cylinder to prevent acidic
26、corrosion in cylinder. 2. Since the exhaust temperature enters the EGR cooler at a lower temperature than the HPL system, the EGR heat transfer surface area required is increased due to the lower entering temperature difference, all other variables being equal. This results in either very closely sp
27、aced tubes (adding coolant side restriction and the risk of localized boiling), or larger space required for the core matrix. 3. Longer EGR piping is required, with more connections and associated reliability risk. Surface heat rejection from the piping to the engine enclosure is also increased, dri
28、ving up engine compartment temperatures or requiring insulated pipes. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 4 of 16 3.2.2 High Pressure Loop EGR FIGURE 2 - HIGH PRESSURE LOOP ERG SCHEMATIC High pressure loop (H
29、PL) EGR is differentiated by its source of exhaust gas taken from the exhaust manifold ahead of the turbocharger. More thermal energy removal is required to reach the desired IMT than LPL architecture which extracts exhaust gas further downstream at a cooler temperature. The cooled gas also contains
30、 all corrosive and abrasive particles before any after treatment is applied. The pre-cooler is again optional, depending on the charge air temperature from the compressor and the temperature limitations of the ATAAC material. Advantages over other Architecture 1. The exhaust piping is simpler, with
31、fewer connections, and associated reliability. 2. Since the exhaust temperature source is at its higher temperature, the heat transfer surface area is reduced to meet the cooler effectiveness requirement, everything else affecting EGR cooler size being equal. Provided by IHSNot for ResaleNo reproduc
32、tion or networking permitted without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 5 of 16 1rst STAGE COOLERCHARGE AIR COOLERAIRFILTEREXHAUSTFILTEROTHER AFTER TREATMENTINTAKEAIRTURBOJWPUMPEGR FLOWCONTROLVALVE2nd STAGE EGRLOW TEMPPUMPDisadvantages over other Architecture 1. Because the exhaust g
33、as enters the EGR cooler at higher temperature, the risk of boiling failure modes is increased. More JW flow is required to prevent boiling on the tubes and tube-header joint at the inlet. This drives increased flow-capacity required from the JW pump. 2. Thermal cycle fatigue within the EGR core mat
34、rix is also a greater risk with the higher differential between hot and cold fluid temperatures. 3. Because the exhaust gas contains abrasive particulate matter, risk of abrasive wear is increased inside the core matrix in areas of high velocity, which may drive material selection of the thin walled
35、 EGR cooler tubes or plates. 4. A third risk related to unfiltered particles in the cylinder intake stream occurs as the exhaust flow enters the cylinder, increasing piston, ring, and liner wear. Finally, fouling of the exhaust side passages will occur to a greater degree than the LPL filtered circu
36、it. Fouling factor, or degradation from new, must be factored in to the design related to heat transfer performance as well as gas side pressure drop. Provisions for cleaning a fouled cooler are also a serviceability issue. 3.2.3 Two Stage EGR Coolant Circuits FIGURE 3 - TWO STAGE EGR COOLANT SCHEMA
37、TIC This third variation illustrates a difference in the coolant side of the EGR architecture. It is applicable to both LPL and HPL configurations, and is independent of the presence of a charge air pre-cooler upstream of the ATAAC. The differentiating feature is that the EGR cooler is a single pass
38、 gas side design, but with two separate coolant circuits passing through the liquid side. The first stage cools the gas in the JW circuit, as in earlier diagrams. But a second, lower temperature coolant circuit, with temperature available below JW thermostat controlled temperature, is used to furthe
39、r lower the exhaust gas, thereby increasing its density and decreasing exhaust port NOx. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 6 of 16 Advantages over Single Stage EGR Cooling 1. The lower temperature of the ex
40、haust at the intake manifold lowers the mixed IMT, and the increased density increases the ratio of EGR flow. Both reduce the NOx content at the exhaust port and reduce the need for further downstream after-treatment. 2. If the IMT goal is equal to the single stage configuration, the lower temperatu
41、re coolant in the second stage increases the overall entering temperature difference T available to the cooler, allowing less surface area and space required for a given heat load removal. Disadvantages over Single Stage EGR Cooling 1. If the overall cooling system already includes a low temperature
42、 circuit with other auxiliary coolers, then there is a small penalty for increased flow capacity for the addition of the EGR cooler second stage. But if the EGR cooler is the only heat exchanger in the low temperature circuit, then the penalties for the addition of a second coolant pump, low tempera
43、ture radiator, and associated water lines add cost, space requirements, weight, and reliability risk. 2. The design of the cooler itself is structurally more challenging since thermal gradients between high and low temperature sections of the cooler are higher than a single stage cooler Another form
44、 of two-stage EGR cooling utilizes a gas-liquid heat exchanger for the first stage, follow by a gas-air cooler for the second stage. Advantages and disadvantages are similar to those already mentioned. One additional disadvantage of this type of system would be the added cost and space for piping of
45、 exhaust gas between the two coolers. Pressure drop limitations on the exhaust gas side would drive up both pipe sizes as well as heat exchanger sizes. The alternative to large line sizes would be higher pressure ratio turbocharging. Provided by IHSNot for ResaleNo reproduction or networking permitt
46、ed without license from IHS-,-,-SAE J2914 Issued NOV2011 Page 7 of 16 3.3 Types of EGR Coolers 3.3.1 Coolant Cooled EGR Coolers 3.3.1.1 Shell and Tube EGR Cooler Gas to coolant shell and tube coolers construction is well documented in other standards. This type includes both round and rectangular tu
47、bes, and is probably the most common choice for EGR coolers, with the gas passing inside the tubes and coolant around the tubes. Several illustrations are provided below in Figures 4 and 5.FIGURE 4 - ROUND TUBE WITH COOLANT SIDE BAFFLE DESIGN The round tube design in Figure 4 with baffles gives a be
48、tter distribution of coolant flow over the tubes at a macro level. But depending on baffle design, eddy currents and low velocity coolant zones within the shell do present a risk of boiling on small areas of the tubes (discussed further in Failure Modes). This risk can be mitigated in the design using CFD. The rectangular tube-shell design in Figure 5, although it is usually designed without baffles, has the same inherent risk of non-uniform coolant flow and localized boiling anywhere in the cooler. A major factor in the distribution of flow over the tubes will be
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