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Optimizing Spark Timing for Enhanced Engine Performance

This activity focuses on understanding how burn duration varies with air-fuel ratio and engine speed. Participants will learn how laminar flame speed influences burn duration and the effect of engine load and speed on timing. The governing equations include the Wiebe function and Annand’s heat transfer prediction method. Students will create a MATLAB function ("timingfunc") to optimize spark timing concerning torque or power output, using a for loop to evaluate a range of spark advance angles. The activity will culminate in plotting the results to visualize performance metrics.

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Optimizing Spark Timing for Enhanced Engine Performance

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  1. Spark-Timing Optimization Activity Learning Objectives Understand how the burn duration changes relative to the air-fuel ratio and engine speed. Describe how the burn duration is influenced by laminar flame speed. Identify how timing is influenced by engine speed and load.

  2. Governing Equations • Weibe Function (constants 3 and 5 are used) • Annand’s Heat Transfer Prediction Method • Apparent Heat Release Model

  3. Choose to optimize spark-timing relative to torque or power. • Place the main MATLAB model within a function (be sure to save the function as the correct name i.e. “timingfunc”) The “function” statement says to input “theta_0” values and output “W_dot_ac” and “T_ac” values. Theta_0 is the spark advance, and W_dot_ac and T_ac are power and torque values, respectively.

  4. Create a script that calls the function. Theta_st and theta_fin specify the range over which timing is optimized. A “for” loop is used to specify each angle over the specified range. Notice that the function is called on the first line inside of the “for” loop.

  5. Specify plotting statements in the call script These plotting statements create plots relative to torque and power outputs.

  6. Specify engine inputs in the main model (shown below). • Comment-out the spark-advance, “clear all”, “close all”, and “clc” within the main model. • Assume a burn duration based on the critical thinking questions.

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