|Achieving Lean Combustion through Trial and Error
| The first thing the AP Lab did was inspect its competitors research on emission control through experiments, as well as to conduct surveys and research. Then it would provide information to the Honda R&D Center.
Surveys were conducted on a variety of possible emissions control methods, from enhancements in gasoline and diesel engine technologies to alternatives such as gas turbines, rotary engines, and Stirling engines. They even studied post-processing devices such as oxidation catalyst and thermal reactors, and alternative fuels such as alcohol and hydrogen.
As part of its promotional efforts the AP Lab put together its own newsletter called AP News, distributing it within Honda R&D Center and associated divisions. The magazine featured information about future changes in work procedures regarding car design, manufacturing, maintenance, and other steps to deal with emissions regulations in Japan and the U.S.
According to Junji Otani, then designer of the Engine-Performance Research Block, Mr. Honda instructed the research engineers to use existing engines. It would be a tremendous task to get rid of existing gasoline engines in an attempt to control emissions, he said. We would have to throw away our entire manufacturing facility. Needless to say, such a measure was not possible. The regulations would simply have to be met with existing engines. Thats why we had to rebuild our current reciprocating engines.
The AP Lab decided to base its emission control research on intake and combustion controls. Since the toxic substances were still released following treatments using other methods, their approach was to treat toxic substances with post-processing devices.
Catalytic converters were at the time being made for stationary facilities, such as factories, to treat smoke emissions. Such devices typically consisted of a tube containing catalytic agents in pellet form. The effectiveness of such a system was thus at a level in which it could comfortably satisfy the 1970 Clean Air Act. However, when attached to an automobile, the device wore thin from vibration or would even burn to a crisp, depending on the quality of combustion. Durability was much in need of improvement.
The team also found that when materials were not completely burned in the combustion chamber, the thermal reactor would reignite them at the emission stage. However, in order to ensure thorough recombustion, a higher air-fuel mixture would be needed. But that decreased the engines fuel efficiency.
Therefore, there had to be some other method they could try. Soichiro Honda had numerous suggestions for the lab, among which were the promotion of fuel vaporization during intake using a new mechanism; and the maintenance of proper intake through a system of fuel injection.
At the time, Tsuyoshi Asanuma, a professor at the University of Tokyo, was paying regular visits to Honda R&D Center once or twice each month as an adviser. The research members would share their opinions with him, and became convinced that the only method to reduce the emission of toxic CO, HC, and NOx altogether was to adopt the lean-combustion method, which would burn the fuel more completely. However, this challenge seemed impossible with the degree of technology that was available to them. However, they remembered a frequent remark by Mr. Honda: What can you learn until you try? And with that, the team began its basic research into lean combustion.
A reciprocating engine operates in the following manner: First, the air-fuel mixture is pressurized in the combustion chamber and ignited. The resulting explosion forces the piston downward, away from the spark. This motion is repeated over and over, being transformed into a rotary motion through the use of a crank. Its a relatively simple process. The stoichiometric mixture ratio for gasoline engines is about 14.7. However, the common blend is higher in fuel than the stoichiometric ratio, because a leaner mixture tends to cause unstable combustion. Accordingly, a mixture that is higher in fuel results in lower gas mileage when compared to an engine that uses the stoichiometric mixture. Since combustion is incomplete, the mixture inevitably generates toxic byproducts. To maintain the proper combination of performance, efficiency and low emissions, it would be necessary to realize a technology that would stabilize combustion at the stoichiometic mixture ratio. Possibly, it should be even leaner than that.
Tests were conducted using every method of measurement imaginable, from heating the mixture and reinforcing the gas movement in the cylinder to increasing the ignition energy and achieving multiple ignitions with several sparkplugs at once. But nothing managed to produce a satisfying result.
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