Table of Contents
Major problems encountered during the design phase:
Load cellDue to intermittent torque spikes that occur when controlling the DC motor, the SM-150 load cell was replaced with the SM-500 load cell as the latter covers a wider operating range.
ThermocouplesFor multiple runs, muffler temperature maxed out at 300 degree F due to the configurations of TC-2095 rack. Changing the DAQ configurations for expected thermocouple voltage output from 100 to 2500mV resolved this issue. A simple experiment with a cigarette lighter was used to verify that higher temperature up to 1300 degree F could be measured.
TFX Analysis SoftwareDuring the installation of pressure analysis software from TFX Engine Technology, we experienced software driver conflict issue for the PC in the operating room (dyne cell). As a result, the DBS 5 data logger could not correctly acquire data from the sensors. To resolve this issue, the TFX analysis software was installed on a different PC. In addition, the PC must meet display resolution requirement of 1028x768 to correctly display the software. An external monitor is typically recommended.
LM-2 Kit/Lambda ReadingsAnother problem encountered was invalid AFR readings from LabVIEW program in comparison to that value displayed by the LM-2 Digital Meter. This was because the LM-2 Digital Meter required connection to USB cable in addition to the power cable for valid voltage output from its configurable analog output channels.
Noise filtration with Simple-Moving Average
Due to high sampling rate of DAQ hardware and "chugging" arising from dyno-scaling and imprecision of dyno controller, simple-moving average (SMA) could be applied to the data during post-analysis with MATLAB to smoothen out short-term fluctuations and highlight long-term trends in acquired data. The period of the SMA is selected as the ratio of the sampling rate of the PCI-6034E DAQ card to the number of samples collected.
IMPORTANT: As pictured below, applying SMA introduces offset between true max values and reported max value as sample points are compressing by averaging. This is expected. Typically, this offset is within -2% to -10% deviation from the true value. However, up to -18% deviation has been recorded. When comparing max values for HP, torque or RPM between two engines, it is recommended that the user disables averaging during post-analysis.
SMA difference of -8.85% for max. torque and -5.31% for max. HP. Also, note differences in reported RPM values.
Validation procedure for all measured parameters is summarized below.
Engine speed in RPM is measured using magnetic encoder during dyno run and an optical encoder during pressure runs. To validate both readings, an inductive tachometer (tiny-tach) is used to measure and correlate the indicate RPM values. From validation, both values matched up very closely with less than -10 to -20 offset in RPM reported by the tiny-tach. This offset is expected as the tiny-tach has an update interval of only 0.5 seconds (2Hz) whereas the NI DAQ system is configured for 1ms (1 KHz).
Engine Output Torque
The SM-500 load cell is calibrated as described in this document. Torque values reported were validated by comparing the measured values to dyno results from Baja Team at Michigan State University.
Temperature Values - Oil, Fin, Carburetor Bowl, Intake Air, Exhaust Gas
As described under Sensors & Data Acquisition, an IR thermometer was used to measure the range of temperature of certain points of interest such as exhaust, engine oil and muffler. The values reported by the thermocouples were validated by comparing the latter to values from IR thermometer. In addition, a block of ice was use to check if the thermocouples could measure 32 degree F (0 degree C).
Cylinder pressure measurements were compared to standard ranges of 1 cylinder engines given a 60-85% volumetric efficiency. The measured values fall within range of the calculated value.
The lambda/AFR value indicated on LabVIEW (back-calculated from output voltage of LM-2 digital meter) was simply crosschecked against values displayed on LM-2 LCD indicator. The engine was ran at critical points (e.g. full throttle etc) in order to achieve lean and rich values. The reported values were crosschecked.
Fuel Flow Rate
The engine was ran at full-throttle to achieve highest fuel flow rate. The indicated fuel flow rate of 1.3gal/hr were checked against expected fuel flow rate of about 1gal/hr observed during races by customer. The values were within range.
Intake Air Flow Rate
The expected maximum intake flow rate for the engine at full throttle was about 20 CFM. This closely matches MAF values of 23 CFM reported over multiple runs.
Sample results & comparison plots from two different dyno runs are available.