SPARK VS COM­PRES­SION

Performance Vauxhall - - FUEL EXPLAINED -

Be­fore we can un­der­stand the ben­e­fits and ad­van­tages de­liv­ered by dif­fer­ent types of fuel, we must first look at how it is used by the host engine. In short, there are two pri­mary types of com­bus­tion engine: spark ig­ni­tion and com­pres­sion ig­ni­tion.

Spark ig­ni­tion is the la­bel given to a petrol engine. These pow­er­plants ig­nite the com­pressed air/fuel mix­ture in the com­bus­tion cham­ber through spark plugs. Com­pres­sion ig­ni­tion is a way of de­scrib­ing diesels, where spark plugs are ab­sent. In­stead, the engine runs a very high static com­pres­sion ra­tio and the fuel (diesel) is of a low oc­tane rat­ing, which al­lows ig­ni­tion with­out a sep­a­rate spark re­quired to ini­ti­ate com­bus­tion.

An­other ma­jor dif­fer­ence worth not­ing is what ef­fect fu­elling con­di­tions have. Most of you will know that a petrol engine run­ning lean – es­pe­cially un­der load – can lead to high op­er­at­ing tem­per­a­tures. This con­di­tion en­cour­ages dan­ger­ously hot ex­haust gases, lead­ing to se­vere engine dam­age. It is with this in mind that many tuners al­low their mod­i­fied en­gines to run de­lib­er­ately rich in a bid to pro­mote re­li­a­bil­ity.

As far as diesel en­gines are con­cerned, the leaner they run, the cooler they be­come. In fact, all diesels run lean in fac­tory spec­i­fi­ca­tion, which is one of the rea­sons they’re gen­er­ally more fuel ef­fi­cient than petrol en­gines. On the down­side, in­creas­ing the air/fuel ra­tio to a richer mix would cause a diesel engine to pro­duce un­sightly black smoke (which is what many think of when asked to bring a diesel to mind). Lean run­ning isn’t or­di­nar­ily a prob­lem for diesel en­gines, mean­ing they can run high boost pres­sures when com­pared to those pro­duced by en­gines mak­ing use of spark ig­ni­tion.

The lesser-spot­ted VXr220 Turbo (only sixty were built) isn’t as thirsty as you might think

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.