CTS successfully demonstrated the use of their Ultra-Lean Burn technologies and methods to improve engine combustion efficiency in automotive applications. Their Cadillac CTS achieved 72 MPG using a small engine platform to provide the 40 HP to propel the car at 60 MPH and racing technology to produce the 6 seconds of high power the car requires to get onto the expressway.
Automobile manufacturers attempted lean burn combustion process during the 70’s using pre-combustion chambers to ignite the lean mixtures. Those systems provided a very narrow window of engine operation and failed. The MSD ignition company was founded to create an ignition system to ignite air fuel mixtures leaner than 20:1. The multiple spark discharge was unsuccessful with lean burn, but was very successful with better starting of the engines, improved idle characteristics and it provided a better spark at high RPM.
The centerpiece technology in CTS’s Ultra-Lean Burn process is the Dynamic Spark Ignition (DSI). The long duration plasma discharge has provided the initiation of combustion at air fuel ratio’s greater than 64:1 AFR with gasoline.
The common understanding of lean burn is as you go leaner with the mixture the combustion gets hotter and things melt. That is not entirely true. As you go leaner, by adding more air, the fuel particles are more insulated by air, thus they are harder to ignite with the heat from a conventional spark due to the distance from fuel particle to fuel particle. If the millisecond spark does not hit a fuel particle, ignition will not occur and you have a misfire. That is what essentially happens as you run leaner; the temperature begins to elevate, getting closer to the detonation zone. Then one cylinder misfires because the spark didn’t hit a fuel particle. The next cylinder will have to carry the additional load from the misfire and it detonates. Then the engine continues a cascade into more detonation until component fail.
If you could have kept the fuel igniting as you went leaner, you would come to find the combustion temperatures begin to decline. When this happens, combustion can be very steady and lower in temperature. That not only produces lower NOx emissions, it provides fuel savings due to less heat being wasted in the combustion process and the beginning of fuel savings.