Study of Handling Behavior of a Passenger Vehicle after addition of CNG Tank

Objective The objective of this paper is to achieve a comparable handling performance from a vehicle fitted with a CNG tank to that of its gasoline counterpart. A validated CarSim model is run through standard handling evaluation tests before and after the addition of CNG tank. The simulation results are used to compare the handling characteristics of the CNG vehicle with the Base vehicle. Further these results are used to tune the suspension parameters to find an optimum set-up for the actual CNG vehicle. The final parameters are then evaluated in the actual vehicle to verify the study. Methodology A mix of Actual Mule vehicle testing backed by quik Car Sim Model. Full car model is first developed using CarSim by using the parameters of the actual base gasoline vehicle. The modeled vehicle is then tested for standard handling maneuvers such Double Lane Change, Constant Radius Constant Speed and Pulse Input. Further the actual vehicle is run through the exact same tests with the same inputs. The results are used to fine tune the CarSim model for better correlation with the real-world. The model is further used to study the change in vehicle handling performance for a CNG variant of the same vehicle. The handling characteristics obtained are compared with the base gasoline vehicle. Areas in performance which are affected are identified and the suspension parameters are varied based on these areas. The model is run again with different iterations of these parameters and again compared with the base vehicle characteristics. The above iterative process is continued until the handling of both vehicles is comparable. Further, the optimized set-up is used in an actual CNG prototype as a starting point. Results The characterisitcs obtained in the Pulse Input and Constant Radius Constant Speed (CRCS) tests indicate the shift in vehicle balance towards less understeer/more oversteer than the base gasoline vehicle. This is observed through a shift in the peak on the Yaw Gain characteristic as well as the Understeer Gradient observed from the CRCS test. The phase lag observed is greater, which estimates that the CNG vehicle is sluggish and is less predictable due to increased weight at the rear. After tuning the suspension parameters of the vehicle to cope with the increased mass at the rear, the handling is found to be comparable to the base gasoline vehicle. Uniqueness This process of simulation and tuning the vehicle on the model saves vital lead time that goes into actual suspension tuning of a passenger vehicle. This helps in making more Robust Mule Prototype vehicle helps in offset of Design Proto vehicles. Conclusion The characteristics obtained both from the actual vehicles (Gasoline and CNG) as well as the simulated models in Carsim achieve a considerable level of correlation. These results can be used for development of other future CNG variants.