What if you could make air so hot it lights fuel on fire? That is exactly how a diesel engine works. On March 18, 1898, an engineer named Rudolf Diesel received a patent for his new engine design. A patent is a document that protects an invention. Diesel's engine worked differently from gasoline engines. In a gasoline engine, a spark plug creates a tiny spark to ignite the fuel. Diesel's engine skipped the spark entirely. Instead, it compressed air inside a metal tube called a cylinder. When air is squeezed tightly enough, it heats up to over 500 degrees. At that temperature, fuel sprayed into the cylinder burns instantly. This method turned out to be more efficient than using a spark. Diesel engines waste less fuel and produce more power for heavy work. That is why they are used in trucks, buses, ships, and locomotives today. Rudolf Diesel hoped his engine would help small business owners compete with large factories. He wanted ordinary people to have access to affordable power.