Translation SAE 730154 (1973): combustion chamber, spark plug and NOx emissions (Nissan)

In this document

Presentation of the study

This is the French translation (No. 73-93) of an SAE paper (S.A.E. Preprint No. 730154, Detroit congress, 8-12 January 1973) signed by Y. Sakai, H. Miyazaki and K. Mukai, from the central engineering laboratories of Nissan Motor Co. (p. 57, p. 68). The original English text follows the translation p. 68-70.

The study seeks the relationship between the "combustion pattern" and NO emission, by varying the shape of the combustion chamber and the location of the spark plug on a 4-stroke single-cylinder petrol engine p. 57.

Experimental setup

The engine (bore x stroke = 83 x 73.3 mm, displacement 399 cm³, compression ratio 8.5) is coupled to a 30 kW dynamometer (p. 58, p. 68). Eight combustion chambers are tested: wedge, "bathtub", hemispherical, bowl-in-piston, Heron, disc, plus two modified versions (p. 58, p. 65). Gases are analysed by NDIR (CO, CO2, NO) and FID (HC) p. 58.

Main results

A 10° ignition timing retard reduces Pi by 4-6%, HC by 20-30% and NO by 30-50% p. 59. Exhaust gas recirculation (EGR) at 10% reduces NO by 60 to 80% p. 59.

With the spark plug in the normal position, NO peaks between 2900 and 3070 ppm depending on the chamber; with a secondary location, the range falls to 2070-2540 ppm p. 59 — the spark plug location therefore appears more decisive than the chamber shape. In return, tolerance to lean mixture and EGR is reduced, and the cycle-to-cycle variation of peak pressure increases from 7-10% to 11-14% p. 60.

Discussion and appendix

The authors link the drop in NO to a lower peak combustion temperature (20 to 50 K lower with the displaced spark plug) p. 60, confirmed by figure 9 linking peak temperature and NO concentration p. 61. A calculation model based on the Wiebe law (equation A-1) confirms that a moderate initial rate of heat release limits NO without penalising power (Pi) too much p. 63-64.

The final summary recalls that these results, obtained on a single-cylinder with homogenised mixture, must be supplemented by other factors (intake, turbulence, atomisation) for a real multi-cylinder engine p. 62.

Context

This SAE paper is part of the context of automotive anti-pollution regulations which were significantly tightened in the United States in the early 1970s (federal standards on NOx, CO, HC). Japanese manufacturers, including Nissan, were then investing heavily in combustion research to meet these constraints without relying solely on downstream exhaust gas treatment (catalytic converter, still in its infancy at that date).

At Citroën, this period corresponds to reflections on "clean" injection and carburetion, in a context where Paul Magès, more of a specialist in hydropneumatic suspension, also followed technical developments affecting engine design and depollution, as evidenced by the creation of a file of translations of foreign technical articles.

Archivist's view

This translation is part of a set of technical documents translated or compiled around carburetion, injection and depollution, probably gathered by the Citroën design departments to follow international literature on the subject. The presence of handwritten annotations in blue pencil (underlining, cross-references "see p.6", "see 5") on several pages p. 58, 61, 62 suggests active and critical reading by an engineer, probably to extract the salient points — likely the relative importance of the spark plug location compared to the chamber shape.

This document is linked to a larger set of translations of technical articles that Magès or his collaborators may have consulted in their research on combustion and anti-pollution, to be compared in particular with the translation of the ATZ 1973 article on the K-Jetronic or the text by Chapoux (UTAC) on anti-pollution action, which testify to the same interest of the time in technical solutions to new environmental constraints.