Ultra Low PM, Naturally Aspirated Diesel Engine Development Meeting Off-Highway Tier IV (Final) Emission Norms 2013-26-0110
To meet stringent US EPA - TIER IV final emission norms, the diesel engine manufacturers are using various technology approaches. These approaches are varying from advanced in-cylinder combustion strategies to sophisticated exhaust after-treatment technologies. Generally, the proven technology concepts such as Common Rail System (CRS), efficient Turbocharged-Intercooled (TCI), and controlled-cooled EGR along with DOC-DPF in after treatment are used for emission controls. However, this approach will increase the engine cost in addition to the Packaging challenges for the existing vehicle layouts.
This paper describes the successful attempt to meet US EPA TIER IV final (<37 kW power category) emission norms on a 2.7 l, Naturally Aspirated (NA) diesel engine for off-highway application. Use of high pressure CRS system, moderate Excess Air Ratio (λ) and optimum engine swept volume selection helped to retain fuel consumption at par with interim TIER IV engine. Open loop, cooled and controlled EGR is used to meet NOx emissions in NRSC, NRTC and NTE limits. Transient smoke control was achieved by optimum design of combustion and EGR system without any close loop control function.
Soot-in-oil type Piston bowl with optimum nozzle spray pattern improved in-cylinder soot burning which in-turn reduced engine out dry soot. Pilot injection and optimum compression ratio reduced engine out Hydrocarbons (HC) even at light load points. Volatile Oil Fractions (VOF) are kept under control by improvement in oil consumption with new ring pack and improved liner honing specifications. Low engine out emissions helped to select lower DOC loading to meet emission targets.
This configuration can be adapted easily in existing vehicle layout which reduced substantial investment in vehicle development. NA engine retains proven advantages of better transient response, 100% block loading capacity and low cost.