Ro­tary-pow­ered cars which made it as far as the show­room.

Classics Monthly - - Contents - Words Iain Wake­field

The Wankel en­gine was a rev­o­lu­tion­ary de­sign that made the re­cip­ro­cat­ing in­ter­nal com­bus­tion en­gine cre­ated by Niko­laus Otto in 1876 seem more like a prod­uct born in the white hot heat of the in­dus­trial revo­lu­tion.

A Wankel en­gine is about as sim­ple as it gets in en­gi­neer­ing terms, as power in a ro­tary pow­er­plant is pro­duced by a troichi­dal shaped ro­tor or­bit­ing an ec­cen­tric shaft in the cen­tre of an epitro­chodal shaped hous­ing.

As the ro­tor or­bits the hous­ing, it cre­ates a large odd shaped com­bus­tion cham­ber and even with two spark plugs fir­ing the mix­ture, not all the fuel is burnt. This leads to a high level of nox­ious fumes ex­it­ing the ex­haust, a sit­u­a­tion that's com­pounded by a ro­tary en­gine's fond­ness to con­sume en­gine oil.

Wankel en­gines are high revving due to the tri­an­gu­lar ro­tor fir­ing three times ev­ery time it or­bits the hous­ing. To lu­bri­cate the hard-work­ing apex seals on the ro­tor's three tips, a small amount of oil is in­jected into the en­gine but this does lit­tle to im­prove the Wankel's rep­u­ta­tion as a 'dirty' en­gine, as sur­plus lu­bri­cant is burned in the com­bus­tion process.

The apex seals on the ro­tor tips work like pis­ton rings in a con­ven­tional re­cip­ro­cat­ing pis­ton en­gine and have to pro­vide a gas tight seal under ex­treme pres­sures and tem­per­a­tures. Fail­ing apex seals are the pri­mary rea­son a Wankel en­gine has to be re­built and back in the late 1960s pre­ma­ture seal wear on the fu­tur­is­tic look­ing NSU Ro 80’s twin-ro­tor power unit proved a mas­sive prob­lem that es­sen­tially bankrupted the com­pany.

Over the years sev­eral ve­hi­cle man­u­fac­tur­ers have in­vested mil­lions of dol­lars and no doubt an equal amount of man-hours re­search­ing and re­fin­ing the Wankel in­ter­nal com­bus­tion en­gine. These com­pa­nies in­clude Citroën with its Ami-based sin­gle ro­tor pow­ered M35 and Chevro­let with an in­ter­est­ing look­ing quad-ro­tor Aerovette XP-985. In the 1970s Mazda built a Wankel pow­ered pickup truck mar­keted as ‘The Pickup with Pickup’, while Rolls-Royce de­vel­oped a two-stage ro­tary en­gine with low and high pres­sure ro­tors.

Other ap­pli­ca­tions in­cluded Cur­tis-Wright Wankel air­craft en­gines and back on terra firma NSU and Nor­ton pro­duced ro­tary pow­ered mo­tor­bikes. A host of small air-cooled ro­tary en­gines have pow­ered snow­mo­biles and chain­saws and in 1991 Mazda won Le Mans with the 787B Wankel pow­ered racer. Sev­eral ro­tary pow­ered Mazda sa­loons also went racing and in 1970 Mercedes-Benz pro­duced a con­cept C111 with a fuel-in­jected four-ro­tor Wankel en­gine. Al­though we’re un­likely to see the launch of a new Wankel pow­ered car in the near fu­ture, the ro­tary en­gine could make a come­back in a range of hy­dro­gen fu­elled hy­brids.

A Wankel en­gine is at its most ef­fi­cient when run­ning at a con­stant speed and back in 2010, Audi ex­per­i­mented us­ing a com­pact 110bhp Wankel unit in its A1-Etron hy­brid con­cept to ex­tend the range of the bat­ter­ies. Al­though a new gen­er­a­tion of bi-fu­elled Wankel en­gines could be used to gen­er­ate power in fu­ture hy­brid ve­hi­cles, the fol­low­ing pan­els de­scribe the main ro­tary pow­ered cars that ac­tu­ally went into pro­duc­tion.

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