Why hasn't someone invented a fuel injection system that only uses the vapors from the gas instead of liquid?

Answer 1

One word - BOOM. But hey, don't let that stop you from making a breakthrough discovery. Actually, someone tried to make a device like this that was said to get 100 mpg. It used the car's coolant to heat the gas to the vapor state. Here's even more:

For example, in 1932, Canadian Charles Nelson Pogue invented a carburetor that was tested by Ford and Winnipeg Motor Company of Canada. Instead of using conventional methods of delivering liquid gasoline into the engine, he created a superheating device that first boiled the fuel into a dry vapor. It was documented that his system got over 200 mpg. It sent shock waves through the Stock Market as oil shares plunged at the announcement of the results. The carburetor was never produced and, mysteriously, Pogue became a wealthy manager of an oil filter company.

Fast forward to the 1970s, and the first of the gasoline shortages. In El Paso, young inventor Tom Ogle claimed that he got over 100 mpg in his “Oglemobile”, a Ford V8 equipped with his fuel vaporizing system. Articles in the El Paso Times reported on his invention including test drives of the Oglemobile. It also reported that a Shell Oil Co. representative asked him what he would do if someone offered him a very large sum of money -- reportedly $25 million. He said he wasn’t interested and was going to bring his invention to market. Unfortunately, shortly afterward Mr. Ogle died. Reportedly he succumbed, either from a drug and/or alcohol overdose.

Just search on 100 mpg carburators for even more results.