Thermodynamic equation for combustion in a spark ignition engine

Click For Summary
The discussion highlights the complexity of determining the pressure exerted on pistons during combustion in a spark ignition engine, emphasizing that numerous variables must be considered beyond just calorific value and volume. Factors such as compression ratio, spark timing, fuel composition, and engine design significantly influence combustion pressure. A rough estimation method suggests that peak combustion pressure can be approximated as 75% of the maximum pressure occurring around 13 degrees before top dead center, although this approach is criticized for its lack of accuracy. Practical tests are recommended to obtain reliable data due to the many assumptions involved in theoretical calculations. Ultimately, precise pressure determination requires a comprehensive understanding of various engine dynamics.
chhitiz
Messages
221
Reaction score
0
if i have calorific value of mixture, volume at time of compression, bore diameter, can i know the pressure being exerted on the pistons due to the combustion?
 
Engineering news on Phys.org
No, there are lots more variables here, sorry. Think about compression ratio, stroke, spark timing, burn delay, end gas temperature, fuel composition, fuel temperature, fuel mixing ratio, engine speed, torque, piston bowl design, cylinder head design, thermal conductivity of the block, piston and head, air fuel ratio, expansion ratio...
 
Plug and chug baby. This is precisely the reason for practical tests.
Short of making lots of assumptions, there is no way to have an equation to show the pressure.

A VERY rough and ready method is to constuct an air standard cycle, and simply assume that the peak combustion pressure is 75% of maximum, that occurs approx 13 deg aTDC.

Disclaimer: I cannot stress just how 'pulled out of the backside' this method is. But it's good if you really are stuck for a better option. This is similar to a method they used in the 1930s to design piston engines aircraft (I can't remember the name of the book that the method was in)
 

Thread 'UV filter for home central heating?'

Had my central air system checked when it sortta wasn't working. I guess I hadn't replaced the filter. Guy suggested I might want to get a UV filter accessory. He said it would "kill bugs and particulates". I know UV can kill the former, not sure how he thinks it's gonna murder the latter. Now I'm finding out there's more than one type of UV filter: one for the air flow and one for the coil. He was suggesting we might get one for the air flow, but now we'll have to change the bulb...
View full post »

Similar threads

Automotive Loss of gaseous volume because of fuel combustion
  • · Replies 2 ·
Replies
2
Views
2K
Pressure/force calculation for combustion in a cylinder
  • · Replies 2 ·
Replies
2
Views
4K
Automotive The reason for the low efficiency of the ICE - zero shoulder crankshaft
  • · Replies 13 ·
Replies
13
Views
2K
Automotive Spark length of a points ignition compared to an HEI system
  • · Replies 7 ·
Replies
7
Views
3K
Pressure generated from gasoline combustion
  • · Replies 5 ·
Replies
5
Views
2K
Automotive Ozone Enhanced Combustion of Water/Diesel Emulsion in CI Engines
  • · Replies 6 ·
Replies
6
Views
2K
How does a 4-piston, 4 stroke internal combustion engine work?
  • · Replies 11 ·
Replies
11
Views
4K
Automotive Flash Point of Petrol & Diesel: Pressure & Self Ignition
  • · Replies 16 ·
Replies
16
Views
4K
High School Deuterium combustion within inertial fusion schemes
  • · Replies 11 ·
Replies
11
Views
2K
A practical way to vaporize fuel for high MPG?
  • · Replies 35 ·
2
Replies
35
Views
2K