Evaluation of a Narrow Spray Cone Angle, Advanced Injection Timing Strategy to Achieve Partially Premixed Compression Ignition Combustion in a Diesel Engine

Abstract
Simultaneous reduction of nitric oxides (NOx) and particulate matter (PM) emissions is possible in a diesel engine by employing a Partially Premixed Compression Ignition (PPCI) strategy. PPCI combustion is attainable with advanced injection timings and heavy exhaust gas recirculation rates. However, over-advanced injection timing can result in the fuel spray missing the combustion bowl, thus dramatically elevating PM emissions. The present study investigates whether the use of narrow spray cone angle injector nozzles can extend the limits of early injection timings, allowing for PPCI combustion realization. It is shown that a low flow rate, 60-degree spray cone angle injector nozzle, along with optimized EGR rate and split injection strategy, can reduce engine-out NOx by 82% and PM by 39%, at the expense of a modest increase (4.5%) in fuel consumption. This PPCI strategy has the potential for meeting upcoming stringent fuel specific NOx emission levels of less than 1 g/kg-fuel and fuel specific PM levels less than 0.25 g/kg-fuel.

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