Com­bus­tion cham­ber de­sign

Ad­vances in soft­ware are al­low­ing de­sign engi­neers to quickly op­ti­mise an en­gine’s abil­ity to gen­er­ate power


WHAT HAP­PENS in­side the cylin­ders of an in­ter­nal com­bus­tion en­gine isn’t an easy process to com­pre­hend. Ex­plod­ing pres­surised air and fuel makes for a hos­tile en­vi­ron­ment, and it’s con­tained in inches of cast metal. Yet un­der­stand­ing how these re­ac­tants move as valves open and pis­tons re­tract is in­cred­i­bly use­ful if you want to de­sign an en­gine.

De­ter­min­ing the per­fect an­gle for the valves and the op­ti­mum po­si­tion for a spark plug isn’t guess­work any­more, but that’s only be­cause years of test­ing and end­less pro­to­types have helped in­form en­gine de­sign­ers. To­day, how­ever, Com­pu­ta­tional Fluid Dy­nam­ics, or CFD, is used to pro­vide an in­sight into the flow pat­terns of liq­uids and gases that are dif­fi­cult or ex­pen­sive to study us­ing tra­di­tional tech­niques, and it can be used to give en­gine de­sign­ers a much more ac­cu­rate idea of how fuel burns and gases flow through an en­gine with­out hav­ing to make pro­to­type parts or spend hours pound­ing a test track.

One com­pany that uses CFD is Il­mor En­gi­neer­ing. Based in Northamp­ton and founded in 1984, Il­mor has been con­tracted to cre­ate en­gines for road car man­u­fac­tur­ers but has also de­signed race en­gines for IndyCar, GT3, WRC and F1.

Il­mor uses a CFD pro­gram called Con­verge (which cre­ated the graph­ics above) to sim­u­late its de­signs. The soft­ware was cre­ated by en­gine spe­cial­ists and is able to rep­re­sent knock­ing/pre-ig­ni­tion and flame prop­a­ga­tion.

Now, you’re prob­a­bly think­ing that once Il­mor has cre­ated the ideal com­bus­tion cham­ber and port an­gles for, say, a four-valve-per­cylin­der head, with or with­out the help of CFD, it can just im­ple­ment that de­sign across all its en­gines. Well, it isn’t that sim­ple. The knowl­edge gained from one en­gine will, of course, in­form an­other, but whether the en­gine is nat­u­rally as­pi­rated or tur­bocharged makes a huge dif­fer­ence on the ideal valve and in­take port an­gles. And, of course, an en­gine’s lay­out will dic­tate what can be achieved. So the CFD soft­ware is used to find the op­ti­mal po­si­tion and shape for each el­e­ment in what­ever vari­a­tion.

The soft­ware is also used to op­ti­mise ex­ist­ing en­gines. Il­mor is us­ing Con­verge to im­prove the de­sign of the in­let ports, chambers and pis­ton crowns of the 2.2-litre twin-turbo Chevro­let V6 it builds for IndyCar. Il­mor says this saves eight weeks of de­vel­op­ment time com­pared with us­ing the tra­di­tional method of mak­ing parts and then test­ing them on a dy­namome­ter.

How­ever, even with the abil­ity to ac­cu­rately sim­u­late com­bus­tion­cham­ber dy­nam­ics, Il­mor hasn’t seen huge power im­prove­ments from us­ing CFD, rather a series of small gains in per­for­mance and ef­fi­ciency. And de­spite the abil­ity to be far more ex­per­i­men­tal and try more rad­i­cal ideas, Il­mor hasn’t learnt any­thing that has rev­o­lu­tionised the way it builds en­gines. But that doesn’t mean the soft­ware isn’t use­ful or pow­er­ful enough – Il­mor’s engi­neers find the data in­valu­able for con­firm­ing what they al­ready know from the com­pany’s 30 years of ex­pe­ri­ence, and it’s saved them count­less hours and tons of alu­minium.

There’s no need to make

pro­to­type en­gine parts or spend hours pound­ing a test track

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