Direct Injection Gasoline (DIG) Injector Deposit Control with Additives

Additive control of DIG injector coking was investigated on two dynamometer-operated engines and validated in a vehicle. The first engine was a Nissan research “mule” engine designed to severely coke the injectors so that additive effect could be more easily discriminated. Initial additive screening and optimization was carried out in this engine and a few chosen candidates of the Mannich chemistry-type were further optimized in the second engine, and in a vehicle. The second engine, which was also dynamometer operated, was an advanced wall-guided design capable of both homogeneous and stratified operation. On this engine we were able to optimize the Mannich additive “Man C-2” separately in two different carrier systems to show a carrier effect, and by manipulating the purity of the base detergent Man C-2 to show a detergent activity modulation by trace co-products. The best optimized formulation on this engine labeled as “Man C-2 (1)a” gave a total injector flow loss of only 0.17% after a combination test cycle of 50 hours homogeneous followed by 50 hours stratified operation. Examination of additive performance in each phase of the test cycle showed one formulation, Man C-2 (1)b, that not only prevented coking in the stratified mode, but also cleaned-up by 26% of the deposit from the preceding phase that was manifested in a homogeneous flow loss of 1.67%. A second Mannich chemistry additive, EM-1 previously reported upon in work carried out in the Nissan research “mule” engine was tested in a prototype DIG vehicle with a spray-guided combustion system. The Mannich Additive EM-1 achieved a complete keep-clean and clean-up injector performance on this DIG vehicle.