Triple Injection Widens Gasoline-Diesel Operating Range

Gasoline direct-injection diesels are highly sensitive to changes in initial gas temperature, initial pressure and exhaust gas recirculation ratios. Thus they must be held to a narrow operating range to meet emission and fuel efficiency goals.

But researchers at the University of Wisconsin-Madison and General Motors Co. who identified those sensitivities also found a solution, at least for an engine running at full throttle: switching from two- to three-pulse injection. The team reports lab results with a single-cylinder test engine in SAE paper 2012-01-1131 available HERE.

The results show that triple-pulse injection can extend the low emissions characteristics of two-pulse injection to full-throttle conditions at high speeds. The team says the second pulse controls combustion stability and maximum pressure rise rate. The third pulse can control engine operation load.

The researchers say that decreasing the EGR ratio tends to narrow the operating timing range of the third pulse. The same effect occurs when the EGR ratio is lowered simultaneously with higher initial gas temperature. Increasing the injection pressure significantly reduces soot emissions.

Future research will looks at the effects of a triple-pulse strategy at lower engine loads, according to the team.