- Author
- Carrier, G. | Fendell, F. | Fink, S. | Feldman, P.
- Title
- Heat Transfer as a Determent of End-Gas Knock.
- Coporate
- TRW Space and Technology Group, Redondo Beach, CA
- Report
- WSS/CI 83-30,
- Book or Conf
- Combustion Institute/Western States Section. Spring Meeting, 1983. April 11-12, 1983, Pasadena, Ca, 70 p., 1983
- Keywords
- heat transfer | internal combustion engines
- Abstract
- Compressive preheting of the residual charge in an Otto-cycle-type, internal-combustion-engine cylinder can result in autoignition and rapid homogeneous burning (explosion). That is, the final portions of the combustible premixture may convert exothermically to product so rapidly that reaction time may be less than acoustic-adjustment cous. In such cycles, large spatial nonuniformity in the pressure field, and onset of knock, result--events potentially damaging to cylinder components. Since operation at high compression ratio is thermally efficient, and since use of knock-inhibiting fuel additives is environmentally constrained, design of combustion-chamber shape to achieve enough heat transfer for smooth flame propagation without knock (or quench) is studied. Specifically, a three-zone model of the nonisobaric combustion event in a variable-volume enclosure is developed. The three zones contain the burned gas, the bulk unburned charge, and the residual unburned charge; the zones are distinguished by the locally applicable polytropic relations, indicated to be a tractable means of parametrically introducing heat transfer into this highly simplified unsteady one-dimensional model. The results indicate that augmented heat transfer from the end gas can prevent those temperatures arising in the residual charge for which autoconversion is likely for plausible input (e.g., for plausible specification of flame speed as function of thermodynamic state of the unburned gas about to be burned). However, at moderate engine speed (~ 2000 rpm), if ignition and final burn-up occur roughly symetrically with respect to piston-crown displacement from top dead center, for the prevention of knock, the fraction of the combustible mass that must be regarded as end gas (and subjected to enhanced cooling by heat transfer) appears to be about one-half.