The Effect of Elliptical Nozzle Holes on Combustion and Emission Formation in a Heavy Duty Diesel Engine

A serie of experiments were carried out to compare the combustion and emissions characteristics of a diesel engine using non-circular (elliptical) and circular shaped fuel injector nozzle holes. Elliptic nozzle holes have the potential to increase air entrainment into the spray, which could lead to decreased emissions from diesel combustion. Previous work [6,7] has shown some interesting results in a passenger car diesel engine and also in a single cylinder engine with optical access. The idea is based on results from investigations of gas jets, where the air entrainment for elliptical jets was increased substantially compared to circular jets. The present series of experiments were carried out to further investigate these effects. The non-circular holes, which were made with an aspect ratio of close to 2:1, have a similar flow rate as the conventional circular holes. Two different angles of the elliptical major axis to the injector centerline were used. The elliptical holes have sharp inlets and the circular holes have rounded inlets. The nozzles were tested at several different loads and speeds in a 2 liter, 4 valve, single-cylinder diesel engine. The engine is based on a Volvo production engine, equipped with an electronically controlled unit injector with variable injection timing. Combustion parameters and emissions are compared for the different holes. It is shown that at certain loads and speeds, elliptical holes can improve substantially the fuel consumption/NO_x trade-off.