fix bugs in CHP unit

[codecov[bot]]

Codecov Report

Merging #89 (1698f73) into main (a1ec6fa) will increase coverage by 0.08%. The diff coverage is 74.07%.

@@            Coverage Diff             @@
##             main      #89      +/-   ##
==========================================
+ Coverage   75.32%   75.41%   +0.08%     
==========================================
  Files          85       85              
  Lines       14532    14523       -9     
  Branches     1592     1590       -2     
==========================================
+ Hits        10946    10952       +6     
+ Misses       3128     3112      -16     
- Partials      458      459       +1     

Flag	Coverage Δ
unittests	75.41% <74.07%> (+0.08%)	:arrow_up:

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Impacted Files	Coverage Δ
qsdsan/sanunits/_combustion.py	76.92% <74.07%> (+6.33%)	:arrow_up:

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[yalinli2]

looks good now, will merge it in!