Adapting the NADI™ concept to heavy duty engines

Abstract

Diesel combustion is well adapted for heavy duty engines but the challenge is twofold. On the one hand, the trade off between NOx and particulate emissions has to be improved. On the other hand, efficiency needs to be maintained and the trend is to increase specific power and torque output. If SCR technology is ready to meet Euro IV and beyond, homogeneous charge compression ignition (HCCI) or highly premixed combustion (HPC) are new technologies that also offer great potential for meeting future NOx and particulate emissions regulation targets. In response to the challenges that the Diesel engine faces, IFP has developed a combustion system which is able to achieve near zero particulates and NOx emissions while maintaining the performance standards of the D.I Diesel engine. This "dual mode" engine application called NADI™ (Narrow Angle Direct Injection) applies Homogeneous Charge Compression Ignition at part load and switches to conventional Diesel combustion to reach high and full load requirements. Thanks to the financial support from European Commission, the "Hy-SPAC E" project leaded by IFP, was launched in partnership with Daimler Chrysler, Iveco, Delphi, Volvo, Chalmers University (Contract G3RD-CT-2002-00 787) with the aim to adapt the NADI™ concept to heavy duty engines. This paper presents the latest developments of the NADI™ concept on a single cylinder heavy duty engine, and the associated improvements regarding HPC (Highly Premixed Combustion) operating range, CO and HC emissions, fuel consumption and combustion noise. At full load, the NADI™ system is consistent with present Diesel performances with a slight increase in fuel consumption and smoke level. In HPC combustion mode, above mid speed of the ESC cycle, a BMEP of 13 bar was achieved with NOx emissions below 0.3 g/kWh which is 25 times lower than a conventional Diesel engine. The particulate emissions are comparable to the standard engine level. CO and HC emissions were limited and compatible with an oxidation after-treatment catalyst performance. The penalty resulting from the higher intake flow and EGR rate needed to control the HPC combustion can be predicted by air-loop OD calculations. The cooling power for air and EGR is also important to maintain acceptable intake temperature. The way to reduce compression ratio was explored and led to a significantly increase in HCCI range. The mains drawbacks are the cold starting conditions and the increase in fuel consumption. The challenge is now to find appropriate multiple staged injection strategies to extend the HCCI range up to higher load and to be fully compatible with the turbocharger performances and cooler efficiencies. Copyright © 2006, Institut français du pétrole.