[Paper Review] Injection rate of cylinder lubrication oil in large two-stroke marine diesel engines using a common rail lubrication system

Bjørn Christian Dueholm, Jesper de Claville Christiansen+2 more|arXiv (Cornell University)|Jul 7, 2023

Advanced Combustion Engine TechnologiesChemical Engineering3 citations

TL;DR

This study experimentally characterizes the injection rate of a common rail cylinder lubrication system in large two-stroke marine diesel engines using the Bosch rate of injection method. It demonstrates that the system achieves a 1 ms mass flow rise time and predicts injected oil amounts with less than 5% error across a 2–21 mg range, enabling precise, high-frequency dosing to reduce emissions and improve efficiency.

ABSTRACT

This paper investigates a common rail cylinder lubrication system for large two-stroke marine diesel engines using electronically controlled injectors. The system is studied using the Bosch rate of injection measurement technique The common rail injector has a buildup of mass flow of approximately 1 ms as the injector opens until the nozzle is choked from cavitation. Using a highly viscous fluid, the Bosch rate of injection method is able to predict the injected amount with an error of 5% or lower for nearly the entire tested delivery range of 2 mg to 21 mg. Lubrication of cylinder liners and piston rings is a crucial parameter in operating a two-stoke marine diesel engine efficiently. Both over and under lubrication is harmful for the engine, so the ability to accurately dose the cylinder oil is very important. A mass flow build up time of 1 ms promises high accuracy of dosage even down to 2.5 mg per injection. This paves the way for injecting the oil where and when it is needed, which in turn will improve engine performance and lower harmful emissions.

Motivation & Objective

• To experimentally characterize the injection rate of an electronically controlled common rail cylinder lubrication system for large two-stroke marine diesel engines.
• To validate the applicability of the Bosch rate of injection method for highly viscous fluids like marine cylinder lubrication oil.
• To assess the feasibility of precise, low-mass dosing (down to 2.5 mg per injection) using fast-rising mass flow profiles.
• To enable optimized lubrication strategies that reduce particulate matter emissions and operational costs by minimizing over-lubrication.

Proposed method

• The Bosch rate of injection method was applied to measure mass flow using pressure transducers and a calibrated measuring pipe with known cross-sectional area.
• A reflected wave technique was used to determine the speed of sound (1375 m/s) in the system, enabling accurate mass calculation from pressure signals.
• The integration of pressure signals over time, with defined borders (Figure 7), allowed calculation of total injected mass per injection.
• Experiments were conducted at varying ramp times (6.6–7.3 ms) and injection pressures (70 bar), with results validated against actual oil collection on a scale.
• The system used single-hole injectors without return pipes, operating under common rail pressure with electronic control.
• Cavitation in the nozzle was monitored as a key factor for flow choking and spray atomization, critical for effective lubrication.

Experimental results

Research questions

• RQ1 Can the Bosch rate of injection method accurately measure the injection rate of highly viscous cylinder lubrication oil in a common rail system?
• RQ2 What is the mass flow rise time of the common rail injector, and how does it affect spray development and oil delivery precision?
• RQ3 To what extent can the system achieve accurate dosing at low injection masses (e.g., 2–21 mg) relevant for emission control?
• RQ4 How does cavitation in the nozzle influence flow choking and atomization in viscous oil injection systems?
• RQ5 Can the injection profile support advanced lubrication strategies, such as multiple injections per piston stroke?

Key findings

• The mass flow rises in approximately 1 ms before cavitation in the nozzle begins to choke the flow, enabling rapid spray development.
• The Bosch rate of injection method predicted the injected oil mass with an error of 5% or less across the entire tested range of 2 mg to 21 mg.
• The relationship between injected mass and ramp time was approximately linear, simplifying precise dosing control.
• The system demonstrated a rise and fall time of about 1 ms, enabling high-precision, high-frequency injection strategies.
• Cavitation in the nozzle was violent enough to effectively atomize the highly viscous oil, supporting the swirl injection principle for liner coverage.
• The validated method enables accurate dosing down to 2.5 mg per injection, opening pathways for optimized, emission-reducing lubrication strategies.