Preheated Liquid Fuel Injection Concept for Lean Pre-chamber Combustion

The pre-chamber combustion (PCC) concept is a proven lean or diluted combustion technique for internal combustion engines with benefits in engine efficiency and reduced NOx emissions. The engine lean operation limit can be extended by supplying auxiliary fuel into the pre-chamber and thereby, achieving mixture stratification inside the pre-chamber over the main chamber. Introducing liquid fuels into the pre-chambers is challenging owing to the small form factor of the pre-chamber. With a conventional injector, the fuel penetrates in liquid form and impinges on the pre-chamber walls, which leads to increased unburned hydrocarbon emissions from the pre-chamber. In this study, a prototype liquid fuel injector is introduced which preheats the fuel within a heated chamber fitted with an electrical heating element before injecting an effervescently atomized spray into the pre-chamber. The experiments were conducted in a heavy-duty pre-chamber research engine using ethanol as the primary fuel. In the first set of experiments, only the pre-chamber was fueled to investigate the influence of injector operating parameters on the mass of fuel injected and the stability of the fuel flow rate. In the second set of experiments, fuel was supplied to both the pre- and the main chamber to investigate the engine performance at different air-fuel ratios at a fixed intake airflow. As a proof of concept, preheating the fuel prior to injection into the pre-chamber was found to improve the combustion stability with simultaneous reductions in engine-out unburned fuel and carbon monoxide emissions while requiring only low power requirements for effective fuel preheating.