Noise emissions and vibrations

Basically, noise emissions are due to combustion pressure gradient, intake and exhaust flows, shocks between moving parts, components distortion under load and components cyclic excitations.

Thanks to their lower pressure gradient and lower max pressure, SI engines emit less noise than Diesel engines. Pressure gradient is comparable to a shock, while higher max pressure induces higher moving parts distortion and a harder piston slap.

Despite the fact they are more complicated, VCR engines have to present a noise level that is comparable to that of conventional engines. To reach this objective, VCR engines requirements are the same than those of conventional engines:

	a)	A highly rigid and closed main structure (crankcase-motorhead-bearing-girdle assembly) to limit distortions while confining internal noise emissions;
	b)	Highly rigid moving parts presenting a low distortion under load (rods, crankshaft);
	c)	Ultra-small mechanical play between moving parts that are under reciprocating motion;

Conclusion

From the combustion point of view, VCR engines emit less noise than Diesel engines. However, to avoid additional noise emissions due to their complexity, they must remain highly rigid and their design must promote a noiseless operation.

(see: The MCE-5 technology response to VCR engines’ noise emissions challenges)