(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (10) International Publication Number (43) International Publication Date PCT 3 July 2008 (03.07.2008) WO 2008/079548 Al (51) International Patent Classification: [IN/IN]; 6a32, Cedar, Sherwood, Basavanagar, Bangalore, F02D 41/02 (2006.01) Karnataka 560037 (IN). (21) International Application Number: (74) Agent: TOOP, Barbara A.; General Electric Company, PCT/US2007/08491 1 Global Patent Operation, 187 Danbury Road, Suite 204, Wilton, CT 06897 (US). (22) International Filing Date: (81) Designated States (unless otherwise indicated, for every 16 November 2007 (16.1 1.2007) kind of national protection available): AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH, (25) Filing Language: English CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, EG, (26) Publication Language: English ES, FI, GB, GD, GE, GH, GM, GT, HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, KR, KZ, LA, LC, LK, (30) Priority Data: LR, LS, LT, LU, LY, MA, MD, ME, MG, MK, MN, MW, 11/641,204 19 December 2006 (19.12.2006) US MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK, SL, SM, SV, SY, (71) Applicant (for all designated States except US): GEN¬ TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ERAL ELECTRIC COMPANY [US/US]; 1 River Road, ZM, ZW Schenectady, NY 12345 (US). (84) Designated States (unless otherwise indicated, for every (72) Inventors; and kind of regional protection available): ARIPO (BW, GH, (75) Inventors/Applicants (for US only): SIVASUBRAMA- GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM, NIAM, Manthram [IN/IN]; C 106, Mantri Sarovar, HSR ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), Layout, Bangalore 560034 (IN). HOUPT, Paul, Kenneth European (AT,BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, [US/US]; 1050 Avon Road, Schenetady, NY 12308 (US). FR, GB, GR, HU, IE, IS, IT, LT, LU, LV,MC, MT, NL, PL, PRIMUS, Roy, James [US/US]; 1436 Rosehill Boule PT, RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, vard, Niskayuna, NY 12309 (US). SHAH, Sunil, Shirish GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG). [Continued on next page] (54) Title: SYSTEM AND METHOD FOR OPERATING A COMPRESSION-IGNITION ENGINE (57) Abstract: A system includes a controller configured to estimate a brake specific nitrogen oxide emission of an engine based on a plurality of sensed parameters of the engine. The controller is also configured to control one or more control variables of the engine to reduce specific fuel consumption while ensuring compliance of brake specific nitrogen oxide emissions within predetermined limits. Declarations under Rule 4.17: Published: — as to applicant's entitlement to apply for and be granted a — with international search report patent (Rule 4.17(H)) — before the expiration of the time limit for amending the — as to the applicant's entitlement to claim the priority of the claims and to be republished in the event of receipt of earlier application (Rule 4.17(Hi)) amendments SYSTEM AND METHOD FOR OPERATING A COMPRESSION-IGNITION ENGINE BACKGROUND [0001] The invention relates generally to a system and method for operating a compression-ignition engine and, more specifically, for controlling emissions. [0002] Compression-ignition engines, such as diesel engines, operate by directly injecting a fuel (e.g., diesel fuel) into compressed air in one or more piston- cylinder assemblies, such that the heat of the compressed air lights the fuel-air mixture. The direct fuel injection atomizes the fuel into droplets, which evaporate and mix with the compressed air in the combustion chambers of the piston-cylinder assemblies. The fuel efficiency, exhaust emissions, and other engine characteristics are directly affected by the compression ratio, the fuel-air ratio, injection timing, ambient conditions, and so forth. Exhaust emissions include pollutants such as carbon monoxide, oxides of nitrogen (NOx), particulate matter (PM), and smoke generated due to incomplete combustion of fuel within the combustion chamber. [0003] Unfortunately, fuel efficiency, exhaust emissions, and other operational characteristics are less than ideal. In addition, conventional techniques to improve one operational characteristic often worsen one or more other operational characteristic. For example, attempts to decrease specific fuel consumption often cause increases in various exhaust emissions. Existing emissions control schemes generally take a conservative approach to ensure emissions compliance, thereby resulting in unnecessarily low fuel efficiency. For example, existing emissions control schemes often use static look-up tables based on previous operational data. Unfortunately, the actual operation of the engine may vary significantly from the static look-up tables, particularly after significant use and wear on the engine and also due to engine power production variation. As a result, the engine exhaust emissions may be at greater or lesser levels than expected by the static look-up tables. Again, the specific fuel consumption is also affected by the emissions control schemes. BRIEF DESCRIPTION [0004] In accordance with one exemplary embodiment of the present invention, a system includes a controller configured to estimate a brake specific nitrogen oxide emission of an engine based on a plurality of sensed parameters. It should be noted that nitrogen oxide emissions include nitrogen monoxide (NO), nitrogen dioxide (NO2), and other oxides of nitrogen. The controller is also configured to control one or more control variables of the engine to maintain the brake specific nitrogen oxide emissions within predetermined limits. [0005] In accordance with another exemplary embodiment of the present invention, a system includes a controller configured to perform closed-loop control of nitrogen oxide emissions of an engine to decrease specific fuel consumption while ensuring emissions compliance of the nitrogen oxide emissions. [0006] In accordance with yet another exemplary embodiment of the present invention, a method includes estimating a brake specific nitrogen oxide emission of an engine based on a plurality of sensed parameters. The method also includes controlling one or more control variables of the engine to maintain the brake specific nitrogen oxide emissions within predetermined limits. [0007] In accordance with yet another exemplary embodiment of the present invention, a computer-readable medium includes programming instructions disposed on the computer-readable medium, wherein the programming instructions include instructions to estimate a brake specific nitrogen oxide emission of an engine based on a plurality of sensed parameters. The programming instructions further include instructions to control one or more control variables of the engine to maintain the brake specific nitrogen oxide emissions within predetermined limits. DRAWINGS [0008] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: [0009] FIG. 1 is a diagrammatical representation of a power unit, such as a locomotive power unit, having engine exhaust emission and specific fuel consumption control features in accordance with an exemplary embodiment of the present technique; [0010] FIG. 2 is a diagrammatical representation of a power unit, such as a locomotive power unit, having engine exhaust emission and specific fuel consumption control features in accordance with the aspects of FIG. 1; [001 1] FIG. 3 is a diagrammatical representation of a turbocharged engine, such as a locomotive power unit, having engine exhaust emission and specific fuel consumption control features in accordance with an exemplary embodiment of the present technique; [0012] FIG. 4 is a diagrammatical representation of engine exhaust emission and fuel efficiency control logic features in accordance with an exemplary embodiment of the present technique; [0013] FIG. 5 is a diagrammatical representation of a system incorporating a turbocharged engine, such as a locomotive power unit, having engine exhaust emission and fuel efficiency control features in accordance with an exemplary embodiment of the present technique; [0014] FIG. 6 is a diagrammatical representation illustrating steps involved in optimization of specific fuel consumption while maintaining emission compliance in accordance with an exemplary embodiment of the present technique; [0015] FIG. 7 is a diagrammatical representation of a Monte Carlo analysis technique configured to estimate sensor accuracy requirements in accordance with an exemplary embodiment of the present technique; [0016] FIG. 8 is a diagrammatical representation of an oxygen based technique for estimation of a brake specific nitrogen oxide emission in accordance with an exemplary embodiment of the present technique; [0017] FIG. 9 is a diagrammatical representation of a control architecture for a brake specific nitrogen oxide emission in accordance with an exemplary embodiment of the present technique; and [0018] FIG. 10 is a flow chart illustrating exemplary steps involved in a process of controlling engine exhaust emission and fuel efficiency in accordance with an exemplary embodiment of the present technique. DETAILED DESCRIPTION [0019] Referring to FIG. 1, a power unit 10 (e.g. locomotive power