Hyundai Developing Diesel Engine
That Runs On Gasoline!
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Your next diesel may run on gasoline!
By Thom Cannell
The Auto Channel
Diesel fuel is powerful stuff, particularly when you compare it to gasoline. Compared to regular 87 octane pump gas it has 30% more BTUs, therefore more power to create heat energy. It also has more carbon molecules than gasoline and that is one of the reasons large and expensive after-treatment devices are fitted to diesel vehicles in the US. Those costs, plus the continuing higher price of diesel technologies like ultra-high injection pressures, multiple stage turbochargers, and piezoelectric injectors is why everyone is looking at building more efficient gasoline engines, or adopting alternative internal combustion fuels like alcohol, DME, natural gas, or hydrogen.
Regardless who is doing the work on these hybrid engines, all began with some basics of modern internal combustion engines: diesel engines operate at very high fuel injection pressures, 1800-2000 Bar, about 29,000 pounds per square inch. Fuel for diesels is directly injected into each cylinder, all modern diesels are turbocharged, and they have relatively high compression ratios. Comparative spark ignition gasoline powered engines increasingly use fuel directly injected into the cylinders but have far lower 100-200 Bar (1400-2900 psi) injection pressures. They also often use turbocharging and have relatively lower compression ratios. You can see that although they are very different, similarities are abundant.
Hyundai, together with Delphi and the University of Wisconsin have developed a running prototype engine, currently based on a production 2.0-liter in-line four cylinder block, that uses both supercharging and turbocharging to create a diesel engine that runs on gasoline. They call it GDCI with PPCI. Which means gasoline direct compression ignition with partially premixed compression ignition. Their engine interweaves the similarities in internal combustion engines.
Stepping back from the heavy metal and technology, futurists say that, in the next 10-30 years, because gasoline is so prevalent, and with the increase in diesel fuel required for greater numbers of heavy duty over the road engines, gasoline remains a fuel for the future.
OK, back to the metal and tech. In Hyundai’s PPCI engine, like all internal combustion engines, fuel is injected—but directly into the cylinder at a compression ratio of 14.8:1, and not until after Top Dead Center where the piston starts moving down into the power stroke. They claim that multiple injections after Top Dead Center result in diesel-like efficiencies and no knock or pre-ignition. This is because an injection of a minute amount of fuel barely after TDC creates sufficient energy to pre-ignite the later injected fuel. It is a very, very lean combustion process due to multiple high pressure injections of fuel. It is also clean and frugal.
While that sounds simple, just squirt the fuel in later, it’s not. The system requires both a supercharger to create early in-cylinder pressures and a turbocharger, plus a large recirculated gas cooler (EGR cooling), and an electrically controlled, constantly variable valve train. Cost savings are achieved using a standard direct injection 200 Bar fuel pump with matched piezoelectric injectors and fuel rail and existing cylinder block.
This technology promises clean burning, low emissions transportation with reasonable price per engine. It also produces more power per cubic inch or centimeter and therefore a smaller, lighter, more fuel efficient engine. Who says diesel, gas, or their marriage is dead?