High load limits of the controlled autoignition engine

The controlled autoignition (CAI) engine is an engine concept that features very low soot and NOx emissions while achieving diesel-like efficiency. The CAI combustion process is characterized by a fast, volumetric burn of a premixed fuel and air mixture that is heavily diluted with either excess air or burned gas. One problem that limits the engine's introduction into the market is that the rate of combustion can be fast to the point that it is very loud and is destructive to the mechanical components of the engine. The nature of this problem is akin to spark-ignition knock and presents a high-load limit to the operating range. Misfire presents a second high-load limit. This work seeks to understand how various engine parameters affect the high-load knock limit and the high-load misfire limit of a CAI engine operating in the negative-valve-overlap mode. Valve timing, and therefore trapped residual gas fraction, turbocharging, intake air heating, and exhaust gas recirculation (EGR) are all explored for their effects on the high load limit. A single-cylinder research engine is used to assess each of these effects. 91 RON gasoline is used for all tests. The first part of the study explores the effects of boost, intake air temperature, and trapped residual fraction on the rate of pressure rise, which was used as the metric for knock, and on NIMEP. It was shown that if operation is constrained by maximum pressure rise rate (PRRmax,,), the maximum load condition always lies at the misfire limit. The dependencies of misfire on boost, intake air temperature, and residual fraction were also explored.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Wildman, Craig B. E. (Craig Bradley Edward), 1987-

Advisor dc:contributor.advisor

• Wai K. Cheng.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/50578

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/50578