The Ford PROCO stratified charge engine combines the desirable characteristics of premixed charge and Diesel engines. The outstanding characteristics of premixed charge engines are their high specific output, wide speed range, light weight and easy startability but they exhibit only modest fuel economy and relatively high exhaust emissions. The desirable characteristic of the Diesel engine is its outstanding fuel economy. However, the disadvantages of the Diesel, which include noisy operation, limited speed range, exhaust odor, smoke, hard startability, and particulate emissions have tended to limit their acceptance. In the gasoline fueled, PROCO stratified charge engine, direct cylinder fuel injection permits operation at overall lean mixture ratios and higher compression ratio. These features enable the PROCO engine to achieve brake specific fuel consumption values in the range of prechamber diesel engines.
The PROCO combustion system includes a combustion bowl in the piston, an intake port designed to impart swirl to the inducted air, a fuel injector nozzle and two spark plugs. A low penetration fuel spray, together with the in-cylinder air motions, provides for excellent mixture preparation under stratified conditions. The injector nozzle is a unique design which provides acceptable atomization with only 250 psi pressure drop. Dual spark ignition facilitates operation with lean air/fuel ratios and high EGR rates which result in NOx control capability coupled with limited HC and CO control. With the use of oxidation catalysts, the engine has the potential to meet the low mileage emission objectives required for certain future emission standards. The fuel injection pump is designed for good cylinder-to-cylinder fuel distribution, control of injection timing over a wide range and fuel delivery vs. speed characteristics which match the engine airflow characteristics. An experimental control system features a modified speed density concept with variable air/fuel ratio control. The unique fuel spray and injection timing schedule result in full air utilization to provide maximum power capability comparable to a premixed charge engine.
In order to maximize the fuel economy at constrained emission levels, mapping tests were conducted on an experimental 6.6L PROCO engine. At eight operating points selected to cover the operating range of urban and highway driving, the air/fuel ratio, EGR rate, injection and spark timings were independently varied. The data obtained from these tests were used to make projections of vehicle results and to define a calibration schedule. The control system was adjusted to this calibration schedule and several engines were installed and tested in vehicles. The results show that the PROCO engine, calibrated to meet the preliminary 4000 mile engineering objectives for the .41/3.4/1.0 gm/mi (HC/CO/NOx) emission standard, exhibits about 20% better fuel economy than the capability of a 1977 baseline vehicle calibrated at the 1.5/15.0/2.0 gm/mi (NC/CO/NOx) emission standard in the same vehicle. Acceleration, power, octane requirement and startability test results were similar to those of a carbureted engine.