Anti-pollution positive-displacement turbocharger: test on a Renault R4 engine (1974)

In this document

The initial observation

The article starts with a problem: existing anti-pollution devices "increase the weight and consumption of engines" p. 45. The author claims that a well-designed system could instead make engines lighter and cleaner, going so far as to mention "400 kg cars with a 50 hp engine" with the performance of large-displacement vehicles p. 45.

The classic internal combustion engine (Beau de Rochas cycle) is presented as superior to diesel engines, Wankel engines, and gas turbines for low power outputs, but its energy efficiency only reaches about 30%, against 35% losses through exhaust gases: "for 1 hp recovered on the engine shaft, about 1.5 hp is dissipated into nature" p. 45.

Classic turbocharger vs. positive-displacement machines

The text explains the principle of the dynamic turbocharger (turbine driven by exhaust gases, actuating a compressor), but highlights its limitations: inefficient on small displacements, and "only efficient in a narrow speed range" p. 45.

Positive-displacement machines are presented as a stable alternative, "the pressure produced is independent of the rotation speed" p. 45-46. The article reviews existing solutions — Roots compressors (instantaneous compression, low efficiency), oscillating vane compressors (speed-limited), and Lysholm screw compressors (heavy, bulky) — to conclude that none are suitable and that it is necessary to "create a positive-displacement machine" with continuous-motion vanes p. 46.

The prototype tested on R4

A positive-displacement compressor prototype was tested on a Renault 845 cm³ R4 engine, reduced to 720 cm³ p. 46. Some numerical data:

The prototype weighed 15 kg, could "be mounted in place of the exhaust pipe", and the engine thus equipped "largely meets anti-pollution standards at all speeds" p. 46. Leaning the mixture combined with valve adjustment would allow for a reduction in specific consumption of about 20% p. 46.

The article finally mentions a future path: a positive-displacement turbocharger with two spiral-grooved stators, driving a rotor through gas expansion p. 46. The handwritten note "Document phase zero" accompanies a photograph of a spiral-grooved part p. 46.

Context

This document is part of the context of the 1970s, marked by the first automotive anti-pollution standards and the 1973 oil crisis, which pushed the industry to seek solutions to reduce consumption and emissions.

The Renault 4, cited as a test bench, was then a popular small-displacement car — a logical choice for studying the applicability of supercharging to small engines, reputed to be poorly suited to the classic turbocharger.

At Citroën, Paul Magès is best known for the hydropneumatic suspension; the interest shown here in positive-displacement supercharging testifies to a broader reflection by the engineer (or his documentary circle) on engine energy efficiency, a subject then highly debated in the technical press.

Archivist's perspective

This document appears to be a technical press clipping kept by Magès as part of a monitoring process on carburetion and depollution — a subject related to his own work on high-precision hydraulic and mechanical systems.

The interest of the document lies in its original proposal: to overcome the limits of the classic dynamic turbocharger through a continuous-motion vane positive-displacement machine, tested concretely on a production engine p. 46, rather than remaining at the theoretical stage.

The handwritten note "74-2132" in the header p. 45 suggests an archival classification probably dating from 1974, consistent with the assigned dating. This document finds a natural echo in other pieces in the same file, notably the handwritten cover page of the file on carburetion and injection and the study by Chapoux (UTAC) on anti-pollution action and fuel economy, which address the same 1974 issue.