{"data":{"id":"us/40-cfr-1048.505","jurisdiction":"us","citation":"40 CFR 1048.505","heading":"How do I test engines using steady-state duty cycles, including ramped-modal testing?","body":"This section describes how to test engines under steady-state conditions. In some cases, we allow you to choose the appropriate steady-state duty cycle for an engine; you may also choose between discrete-mode and ramped-modal testing. In all cases, you must use the duty cycle you select in your application for certification for all testing you perform for that engine family. If we test your engines to confirm that they meet emission standards, we will use the duty cycles you select for your own testing. If you submit certification test data using more than one duty cycle, any of the selected duty cycles may be used for any subsequent testing. We may also perform other testing as allowed by the Clean Air Act.\n(a) You may perform steady-state testing with either discrete-mode or ramped-modal cycles described in 40 CFR Part 1065.\n(b) Measure emissions by testing the engine on a dynamometer with one or more of the following sets of duty cycles to determine whether it meets the steady-state emission standards in § 1048.101(b):\n(1) For engines from an engine family that will be used only in variable-speed applications, use one of the following duty cycles:\n(i) The following duty cycle applies for discrete-mode testing:\nTable 1 of § 1048.505\nC2 mode No. Engine speed 1 Torque (percent) 2 Weighting factors\n1 Maximum test speed 25 0.06\n2 Intermediate test 100 0.02\n3 Intermediate test 75 0.05\n4 Intermediate test 50 0.32\n5 Intermediate test 25 0.30\n6 Intermediate test 10 0.10\n7 Warm idle 0 0.15\n1 Speed terms are defined in 40 CFR part 1065.\n2 The percent torque is relative to the maximum torque at the given engine speed.\n(ii) The following duty cycle applies for ramped-modal testing:\nTable 2 of § 1048.505\nRMC mode Time in mode (seconds) Engine speed 1 2 Torque (percent) 2 3\n1a Steady-state 119 Warm idle 0\n1b Transition 20 Linear transition Linear transition.\n2a Steady-state 29 Intermediate speed 100\n2b Transition 20 Intermediate speed Linear transition.\n3a Steady-state 150 Intermediate speed 10\n3b Transition 20 Intermediate speed Linear transition.\n4a Steady-state 80 Intermediate speed 75\n4b Transition 20 Intermediate speed Linear transition.\n5a Steady-state 513 Intermediate speed 25\n5b Transition 20 Intermediate speed Linear transition.\n6a Steady-state 549 Intermediate speed 50\n6b Transition 20 Linear transition Linear transition.\n7a Steady-state 96 Maximum test speed 25\n7b Transition 20 Linear transition Linear transition.\n8 Steady-state 124 Warm idle 0\n1 Speed terms are defined in 40 CFR part 1065.\n2 Advance from one mode to the next within a 20-second transition phase. During the transition phase, command a linear progression from the torque setting of the current mode to the torque setting of the next mode.\n3 The percent torque is relative to maximum torque at the commanded engine speed.\n(2) For engines from an engine family that will be used only at a single, rated speed, use the 5-mode duty cycle or the corresponding ramped-modal cycle described in 40 CFR part 1039, Appendix II, paragraph (a).\n(3) Use a duty cycle from both paragraphs (b)(1) and (b)(2) of this section if you will not restrict an engine family to constant-speed or variable-speed applications.\n(4) Use a duty cycle specified in paragraph (b)(2) of this section for all severe-duty engines.\n(5) For high-load engines, use one of the following duty cycles:\n(i) The following duty cycle applies for discrete-mode testing:\nTable 3 of § 1048.505\nMode No. Engine speed Torque (percent) 1 Minimum time in mode (minutes) Weighting factors\n1 Maximum test speed 100 3.0 0.50\n2 Maximum test speed 75 3.0 0.50\n1 The percent torque is relative to the maximum torque at maximum test speed.\n(ii) The following duty cycle applies for discrete-mode testing:\nTable 4 of § 1048.505\nRMC modes Time in mode (seconds) Engine speed (percent) Torque (percent) 1 2\n1a Steady-state 290 Engine governed 100\n1b Transition 20 Engine governed Linear transition.\n2 Steady-state 290 Engine governed 75\n1 The percent torque is relative to maximum test torque.\n2 Advance from one mode to the next within a 20-second transition phase. During the transition phase, command a linear progression from the torque setting of the current mode to the torque setting of the next mode.\n(c) For full-load operating modes, operate the engine at wide-open throttle.","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1048—CONTROL OF EMISSIONS FROM NEW, LARGE NONROAD SPARK-IGNITION ENGINES","Subpart F—Test Procedures"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"35198ee7a5fe18e76cb184f2bbcfd801c090acc57c06c81a3fac42296f5338ae","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1048.501","next":"us/40-cfr-1048.510"},"notice":"GroundRules: Original legal text. Not legal advice."}