[aerohead]

I beat up on Mr.Singh pretty good and out of common decency have "dug in" a little to see if there was more to his grooves.My 700+ page textbook on I.C. Engines had little in the INDEX, however I did find data scattered throughout the book and have amended the index for the future.------------------------- While I'm not vindicating Mr.Singh,there is a logic to the argument,however the text contradicts itself.Here's the deal.-------------------------------------- In 1923,Sir Harry Ricardo,England,received a patent for a "turbulent chamber" design for combustion chambers for an L-Head (flathead) engine.The design induced high turbulence near the end of the compression stroke.The turbulence helped scour the mixture close to the chamber walls,creating a more homogeneous mix,knock was reduced with the piston close to the head.Quench space was small,if autoignition occurred,it would have less impact, as end gas mass was small.End gas was cooled by proximity to cooler walls,spark plug was centrally located near the hot exhaust valve to reduce flame path and speed combustion.---------------------------- The design allowed for higher compression ratios without destructive detonation knock.----------------------------------- Combustion flames can be "laminar" or "turbulent".Laminar flames occur inside bomb calorimeters.Turbulent flames occur inside internal combustion engines.( so I don't understand why Mr. Singh refers to laminar flame with respect to IC engines).--------------------------------- Flame speed can be increased many times with turbulence.Turbulence sweeps unburned mixture into the reaction zone.Also,highly convective currents carry active particles into the unburned region.Turbulence can also arise from flame induction from microscopic explosions.Turbulence increases with engine speed.Combustion time is always shortened by autoignition,gives rise to higher pressure leading to knock.Maximum power is obtained when spark timing is adjusted to point of audible knock.---------------------------------- At the time my book was published,there was no way to quantify turbulent flame velocity,no units to work with,and no way to make tables,showing interrelationships as functions of temp,pressure,composition,etc..No scale had yet been discovered.------------------------- The book makes mention that turbulence,induced on the compression stroke is better than turbulence from the intake stroke,as it does not effect volumetric efficiency.(so far so good for Mr. Singh).------------------------ Here are some points to ponder.From the 1st law of thermo,the mixture cannot have any more energy than the constituent components.And since turbulence is nothing new to combustion chamber and piston design,the efficiency gains from turbulence induced by the grooves requires extraordinary proof.----------------------------- With respect to the Metro engine mods,here are a couple of things to consider.Compression ratios for engines are determined on a basis of engine friction.Compression ratio is a "weak" variable as associated with fuel economy.A 10% increase in compression ratio yields only a 2.3% increase in mpg.Increasing the CR also aggravates the formation of both NOx and HC emissions,requires spark timing to be retarded,which leads to extra engine heat,which requires a bigger or faster fan,and larger radiator.Starting requires more power,the engine requires higher octane.--------------------------- In addition,Tetra ethyl lead,formerly used in high compression engines was believed to create a catalytic effect at the combustion chamber walls,preventing the formation of free radicals and peroxides.Today,without TEL,someone else will have to tell us if current octane enhancers serve the same function.I don't have a clue! Altering an engine from factory specs can defeat the emission controls,potentially releasing CO,alcohols,aldehydes,ketones,phenols,acids,esters ,ethers,epoxides,and other oxygenates besides peroxides.------------------------------- Finally,in some cars with automatic transmissions,the engine can never be loaded to the point of explosive detonation,as the trans simply downshifts to reduce the load,something the Metro would not have available(yes?).------------------So it looks like there are kernels of truth to the premise of the grooves,I just don't know what potential gains can be expected if any,and the article is very subjective and not really loaded with useful quanta.Interesting though!