Difficult, yes, but doable: mazda's SKY-D diesel features 14:1 compression and Tier II Bin 5 / Euro VI compliant emissions without Urea. The lower emissions wer

Difficult, yes, but doable: mazda's SKY-D diesel features 14:1 compression and Tier II Bin 5 / Euro VI compliant emissions without Urea. The lower emissions were achieved by lowering the compression ratio and lengthening the exhaust manifold, so that the exhaust gasses can cool. As the result, mazda is the only manufacturer selling diesel passenger cars in Japan.