EPA 2015 Tier IV emission requirements pose significant challenges to large diesel engine aftertreatment system (EAS) development aimed at reducing exhaust emissions such as NOx and PM. An EAS has three primary subsystems, Aftertreatment hardware, controls and fluid delivery. Fluid delivery is the subsystem which supplies urea into exhaust stream to allow SCR catalytic reaction and/or periodic DOC diesel dosing to elevate exhaust temperatures for diesel particulate filter (DPF) soot regeneration. The purpose of this paper is to discuss various aspects of fluid delivery system development from flow and pressure perspective. It starts by giving an overview of the system requirements and outlining theoretical background; then discusses overall design considerations, injector and pump selection criteria, and three main injector layouts. Steady state system performance was studied for manifold layout. The transient pressure fluctuations from injector activations and deactivations were measured by using both pressure gauges and high frequency sampling devices. It is observed that a low pressure common rail demonstrates high level of pressure fluctuations; therefore countermeasures such as hardware changes and control software options were implemented. Along with measurements, CFD models and flow network models were developed and compared to test data. The discrepancy between tests and modeling were analyzed and reviewed. Multiple designs of experiments by tests and modeling were carried out to study specific system performance and design parameters. Recommendations were provided with respect to reducing pressure fluctuations and maintaining stable steady state pressure.