LEV-3 regulation changes require 100% SULEV30 fleet average by 2025. While present applications meeting SULEV30 are predominately small displacement 4-cylinder engines, LEV-3 standards will require larger displacement engines to also meet SULEV30. One concept previously investigated to reduce the cold start engine-out HC emissions was to heat the fuel injected during the cold start and initial engine idle period. Improved atomization and increased vaporization of heated fuel decreased wall wetting and unburned fuel. This resulted in more fuel available to take part in combustion, thus reducing the required injected fuel mass and HC emissions.
Single cylinder engine testing with experimental heated Gasoline Direct Injection (GDi) injectors was conducted at 40°C engine coolant and oil temperature conditions. The operating mode simulated cold start idle operating conditions, with split injection for improved Catalyst Light-Off (CATLO) times. Testing showed that fuel heating increased engine stability at leaner Air/Fuel (A/F) ratios. The leaner A/F ratio operation reduced emissions, particulates and smoke.
These results led to further investigations in a vehicle platform. The method of heating the fuel was altered due to hardware limitations, and pre-heating a fuel rail and GDi injector fuel coils were used to produce a representative fuel stream temperature profile, previously measured with experimental Heated GDi injectors. Heated versus unheated gasoline cold start emission performance was compared on a 3.8L 6-cylinder naturally aspirated vehicle which demonstrated a reduction in HC emissions using heated fuel.
The experimental GDi injectors, single cylinder test results, fuel heating methodology, vehicle installation, engine re-calibration, as well as comparisons of engine-out and tailpipe emissions produced with unheated and heated fuel are presented and discussed.