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SwRI has developed a new technology concept involving the use of high EGR rates coupled with a high-energy ignition system in a gasoline engine to improve fuel economy and emissions. Based on a single-cylinder study [1], this study extends the concept of a high compression ratio gasoline engine with EGR rates > 30% and a high-energy ignition system to a multi-cylinder engine. A 2000 MY Isuzu Duramax 6.6 L 8-cylinder engine was converted to run on gasoline with a diesel pilot ignition system. The engine was run at two compression ratios, 17.5:1 and 12.5:1 and with two different EGR systems - a low-pressure loop and a high pressure loop. A high cetane number (CN) diesel fuel (CN=76) was used as the ignition source and two different octane number (ON) gasolines were investigated - a pump grade 91 ON ((R+M)/2) and a 103 ON ((R+M)/2) racing fuel.

Tests were conducted on a variety of commercially available spark plugs to determine the influence of igniter design on initial kernel formation and overall performance. Flame kernel formation was investigated using high-speed schlieren visualization. The flame growth rate was quantified using the area of the burned gas region. The results showed that kernel growth rate was heavily influenced by electrode geometry and configuration. The igniters were also tested in a bomb calorimeter to determine the levels of supplied and delivered energy. The typical ratio of supplied to delivered energy was 20% and igniters with a higher internal resistance delivered more energy and had faster kernel formation rates. The exception was plugs with large amounts of conductive mass near the electrodes, which had very slow kernel formation rates despite relatively high delivered energy levels.

Swirl plane Particle Image Velocimetry (PIV) measurements were performed in a single-cylinder optically accessible gasoline direct injection (DISI) engine using a borescope introduced through the spark plug hole. This allowed the use of a contoured piston and the visualization of the flow field in and around the piston bowl. The manifold absolute pressure (MAP) was fixed at 90 kPa and the engine speed was varied in increments of 250 rpm from 750 rpm to 2000 rpm. Images were taken from 270° to 320° bTDC of compression at 10° intervals to study the evolution of the velocity fluctuations. Measurements were performed with and without fuel injection to study its effect on the in-cylinder flow fields. Fuel was injected at 10 MPa and 5 MPa. The 2-D spatial mean velocities of individual flow fields and their decompositions were averaged over 100 cycles and used to investigate the effects of engine speed and image timing on the flow field.

The use of high levels of EGR has been documented to increase fuel efficiency and reduce emissions of spark ignition engines [1–5]. However, these engines typically face challenges in EGR control and tolerance, which can reduce the expected efficiency improvement. A concept developed by Southwest Research Institute explores the potential of an engine with individual cylinders dedicated to EGR production to overcome the challenges associated with EGR tolerance and control. In this study, a 4-cylinder engine was run with cylinder 1 exhausting directly to the intake manifold, leading to a constant 25% EGR level. The engine was run naturally aspirated over a large portion of the performance map at an ultra-high (14:1) compression ratio. As a part of the study, air-to-fuel ratio in cylinder 1 was varied from stoichiometric to rich to determine the effect of the products of partial combustion on EGR tolerance and fuel consumption.