According to a 1969 article in Commercial Car Journal vol. 117, page 63
One dead, eight injured, when mystery engine explodes in test Development of a mystery automobile engine by Environetics, Inc. of Gardena, Calif., has been deterred following an explosion of the prototype during a demonstration. Designed by Joseph Papp, 35, the engine exploded, according to witnesses, when the designer plugged it into an electrical outlet used as a generating power source. Eight observers were injured and a ninth man died of a heart attack
Also, from the newspaper Independent from Long Beach, California 19 November 1968
Secret Fuel blows up 1 dies 8 hurt A Torrance man died and eight others were injured when experimental low : smog fuel being tested near Â· Gardena exploded Monday. Jack Hartman, 40, of 25010 Anza Ave., died apparently of a heart attack shortly after the 2:30 p.m. explosion of the fuel in a testing engine at the West Coast Refrigeration and Fixture Co., 15821 S. Broadway. County firemen were dispatched to the firm with radiation detection equipment when first reports of the explosion indicated the fuel contained radioactive elements. Fire Capt. Charles Cornel said ho traces of radioactivity ;_ were found. However, spokesmen for the Â· firm refused to disclose to officials the chemical composition of the fuel. Joseph, Papp, 35, inventor of the fuel, said the mixture was being tested in a small foreign auto engine.
Also, from the same newspaper Independent from Long Beach, California 20 November 1968, page 3
Man Hunted in Gardena Blast Death The sheriff's arson squad Tuesday, sought for questioning a man suspected of causing the explosion of an experimental engine in Gardena which killed an engineer and injured three other persons. The man sought was. a bystander at the Monday blast which rocked Environetics Inc., 15821 S. Broadway, and killed Jack Edward Hartman, 40, of 21010 Anza Ave./Torrance. Witnesses said the man shouted "this demonstration is a fraud" and pulled an electrical wire loose from a piece of equipment used in a test running of a modified Volvo powered by a solid propellant fuel cell. The cell's inventor, Joseph Papp, 35, said the action probably caused a pressure buildup in an engine cylinder and triggered the explosion. Joseph J. Quagletll, of Palos Verdes, who was critically injured in the explosion, was reported in improved condition Tuesday in Memorial Hospital in Gardena. An autopsy Is pending in Hartman's death
In the San Bernardino County Sun 19 November 1968, page 20
Explosion Kills Man, Injures 8 GARDENA (AP) - A motor being used to test an experimental fuel exploded yesterday, killing a man and injuring eight others. Although the fuel was radio - active, sheriff's deputies said no trace of radioactivity was found after the blast. Officials at Gardena Memorial Hospital said Jack Hartman, 40, of Torrance, a toy company employee, apparently died of a heart attack. Three others were reported in serious condition at that hospital, where five were treated and released. One man's leg was blown off. The explosion occurred at the West Coast Refrigeration Fixture Co., as 35 persons stood around the engine. The electrical input used to start the small foreign auto engine became disconnected, said the inventor. Joseph Pappp and he walked over to restart the engine when it exploded. Sheriff's officers said the fuel was being developed as a semi - classified experiment for the Navy.
And from the San Bernardino County Sun 21 November 1968:
The explosion of an experimental automobile engine that killed one man and injured eight others: apparently did not involve criminal negligence, sheriff's investigator Harold White said. An unidentified observer who removed the engine's control wires during a demonstration Monday apparently wanted only to assure himself the engine was not working off electricity, deputies said. A pressure buildup exploded the engine. Jack Hartman. 40, of Torrance was dead of schrapnel and a possible heart attack. One of the eight other victims, Joseph Auglclti, 52, of Palos Verdes, remained in critical condition Tuesday.
Two references confirm that Feynman wrote the LASER article, which was titled Mr. Papf's Perpetual-Motion Machine:
The 1989 Skeptical Inquire vol. 14, page 46 (which appears to republished the whole article along with another Feynman article). The articles are introduced on page 45:
The following two stories by Feynman, who died 15 February 1988, did not appear in either of his two popular books, but they are in the same delightful anecdotal style. We are grateful to his longtime friend and literary collaborator, Ralph Leighton, for making them available for publication in SI and to Al Seckel of Southern California Skeptics for first drawing our attention to them. They were first published in the SCS newsletter LASER (January-March 1989) and were are pleased to bring them to a wider audience.
the 1992 book Magill's Survey of Science: The Michelson-Morley experiment-Planetary magnetospheres at page 1775.
The late Dr. Feynman is recognized as a fine teacher, writer, and scientist; this is a report of his encounter with the inventor of an automobile that ... The last line tells it all: "And, of course, nothing has been heard of Mr. Papf 's new engine since."