INTAKE-AIR OXYGEN-ENRICHMENT OF DIESEL ENGINES AS A POWER ENHANCEMENT METHOD AND IMPLICATIONS ON POLLUTANT EMISSIONS

摘要

Increasing the in-cylinder oxygen availability of diesel engines is an effective method to improve combustion efficiency and to reduce particulate emissions. Past work on oxygen-enrichment of the intake air, revealed a large decrease of ignition delay, a remarkable decrease of soot emissions as well as reduction of CO and unburned hydrocarbon (HC) emissions while, brake specific fuel consumption (bsfc) remained unaffected or even improved. Moreover, experiments conducted in the past by authors revealed that oxygen-enrichment of the intake air (from 21% to 25% oxygen mole fraction) under high fuelling rates resulted to an increase of brake power output by 10%. However, a considerable increase of NOx emissions was recorded. This manuscript, presents the results of a theoretical investigation that examines the effect of oxygen enrichment of intake air, up to 30%v/v, on the local combustion characteristics, soot and NO concentrations under the following two in-cylinder mixing conditions: (1) lean in-cylinder average fuel/oxygen equivalence ratio (constant fuelling rate) and (2) constant in-cylinder average fuel/oxygen equivalence ratio (increased fuelling rate). A phenomenological engine simulation model is used to shed light into the influence of the oxygen content of combustion air on the distribution of combustion parameters, soot and nitric oxide inside the fuel jet, in all cases considered. Simulations were made for a naturally aspirated single-cylinder DI diesel engine "Lister LV1" at 2500 rpm and at various engine loads. The outcome of thisrntheoretical investigation was contrasted with published experimental findings.