Figure 7 - Full-load power pull, X-axis equals time (in seconds), Y-axis equals CO emissio
It may be seen in Figure 5 that lambda varies from approximately 0.82-0.87 for a majority of the configurations, with greater inconsistency occurring for the carbureted induction system. These relative A/F ratios were established to maximize power in the calibrations for the fuel injection induction systems, and were simply observed from the carburetor tests (after tuning the jets for near maximum torque). From this, many conclusions can be made.
Reviewing the cycle-weighted emissions in Figure 6, we see that there is actually a very modest reduction in CO/HC relative to the engine not utilizing a catalyst (for the 100-octane fuel), and an actual increase in HC emissions for the E85 FI engine when using the catalyst.
However, there is measurable NOx reduction for all cases utilizing the catalysts. In order to shed light on these results, the global chemical reactions for CO/HC oxidation and NOx formation/reduction are provided in the purple box.
Since the reactions required for the catalyst to properly function require a near stoichiometric A/F charge mix (approximately 14.7:1 for gasoline), it's clearly seen from these reactions that there is insufficient O2 in the exhaust stream for the converters to have a high conversion efficiency of unburned HC and CO when the engine is running a rich A/F equivalence ratio. Also from these reactions, we can see that in order to reduce NOx, diatomic O2 is not required. Therefore, the catalyst is effective for NOx reduction. Further evidence of this can be seen in Figures 6, 7, and 8. By comparing the full-load sweep measurements of HC, CO, and NOx emissions over the full-load pull, at best we see only modest oxidation of CO and HC, even though the 300-CPI catalyst had three times the cell count and reactive surface area of the 100-CPI catalyst.
In theory, significant oxidation would have been achieved if the exhaust stream had the proper composition of air and fuel. Because the engine was calibrated for peak torque across its entire operating range (or the carburetor tuned for peak power), additional O2 in the exhaust stream would have been required to improve catalytic convertor efficiency. This topic will be covered further in future testing as the team heads to the track.
How would the engine respond to a switch from conventional racing gasoline to E85?
In the May issue of CT we covered the base engine testing that was conducted at Mast Motorsports, comparing the 100-octane conventional race fuel to E85 in some detail. From those results, there was (as anticipated) a significant gain in torque from the 93- to 100-octane fuel, with another slight gain in torque from 4,000 rpm to approximately 6,250 rpm for the E85-fueled configuration. These tests were all conducted with the electronic fuel-injection induction system. However, it's here noted that the calibrations were not fully optimized for the E85 fuel due to time constraints.
Referring back to Figure 5, one can see that the fueling rate for E85 was slightly lean relative to the race fuel counterpart, resulting in non-optimal maximum brake torque calibrations. This would have resulted in slightly higher torque values than those presented. That said, the high heat of vaporization of E85 relative to 100-octane race fuel suggests increased in-cylinder A/F charge densities. Also, burn curve characteristics of the E85 fuel, coupled with reduced heat transfer rates (due to the cooler intake charge) would also increase the overall power potential.
For the first round of testing, in-cylinder pressure measurements and the corresponding heat release rate data were not available. The CT team is in the stages of planning a second round of engine testing that will include individual cylinder pres-sure measurements, which will provide us with detailed combustion information for an improved understanding of the actual burn process and the thermodynamics involved. The results will be published in the future, as this project continues to unfold.