Over the past 24 months, Ford Motor Company has made major commitments to the future of its battery-electric vehicle business. The company announced on-demand production increases for its two BEVs, the Mustang Mach-E and the upcoming F-150 Lightning pickup truck. Plans for two battery plants in Kentucky and one in Tennessee are detailed, in addition to BEV’s large Tennessee campus. More significantly, the company is planning an internal restructuring that separates its internal combustion and electric vehicle programs into separate silos. Amid all the high-profile BEV news, Ford engineers are quietly looking for ways to keep the internal combustion side of the business healthy, including a new method of burning hydrogen.
Found by MC&T In the US Patent and Trademark Office database, Ford has created a combustion method that allows a turbocharged hydrogen-fueled engine to operate at various air/fuel lambda values depending on torque demands. Internal exhaust gas recirculation (EGR) and valve timing will be used to control combustion.
Lambda is a Greek letter used to represent the stoichiometric value of a fuel as 1.00. The stoichiometric value of the fuel is the ratio at which all the fuel is combined with all the oxygen to produce complete combustion. Gasoline engines have a stoichiometric value of 14.7:1, which means 14.7 parts of air for 1 part of gasoline equals lambda 1. Lean combustion is represented as a value higher than 1.00, while richer mixtures are shown as less than 1, 00.
For the most part, gasoline engines can operate in the range from 8:1 at the richest to 18.5:1 at the lean end of the spectrum. Lambda is calculated by plugging the air/fuel ratio into the stoichiometric value of the fuel – so the richest gasoline-burning mixture is represented as 0.54 lambda, while the leanest is 1.25 lambda. Ford’s new method of burning turbocharged hydrogen is seen exploring lambda values in excess of 2.00. This means the engine will be able to operate in a very lean state, using more than double the amount of air required for the stoichiometric combustion of hydrogen.
Available data indicate the stoichiometric value of hydrogen is in the 34:1 range, so if Ford is running hydrogen combustion on a Lambda of 2.00 or more, that means the engine has an air/fuel mixture of at least 68 parts air to 1 part hydrogen. For what it’s worth, Mike Copeland’s hydrogen-converted LS engine runs at 100:1 with the help of a supercharger. Hydrogen is capable of burning in lean air/fuel mixtures due to the low impedance of the fuel to ignition. At stoichiometric values, hydrogen has a very fast ignition speed, described as being an order of magnitude faster than gasoline. An increase in flame speed means there is a much greater chance of explosion, however, if the mixture is leaner, the flame speed decreases.
For Ford’s hydrogen combustion method to work, hydrogen will be introduced via direct injection, allowing fuel and air to be controlled independently of each other as opposed to using port injection, which mixes air/fuel upstream of the combustion chamber. Supplied using DI, hydrogen is capable of delivering 15% more power than gasoline.
Using a constant fuel input, the EGR amount can be changed to move the post-burn lambda value from 1.00 to 2.00 or higher. Under higher torque demands when the mixture is more hydrogen rich, the EGR flow will be increased to reduce the temperature in the combustion chamber, thereby reducing the possibility of pre-ignition. This is true because the recirculated exhaust gases enrich the hydrogen mixture by displacing the air normally present in the room. Remember, a combustion engine produces maximum power from a slightly richer air/fuel mixture, while a leaner mixture is better for fuel economy. Lean blends contain substantially less fuel than richer ones. When torque demands are lower and the hydrogen engine runs leaner, less EGR will be provided.
According to the patent, the EGR content can be changed by shifting the valve timing or by introducing significant overlap. Ford is looking for a “multi-lift profile” in which “the intake valve performs two mutually independent valve strokes during one duty cycle.” This can be achieved through a “second valve stroke performed before the actual valve stroke of the intake valve.” All of this will be controlled by a fully variable valve controller capable of changing the duration and stroke of the valve.
Lastly, Ford claims a hydrogen combustion engine could be part of a hybrid powertrain. Examples shown include a motor-generator unit placed in series between the engine and transmission, but Ford claims it can be used in parallel, series, or series-parallel hybrid vehicles. Pairing the hydrogen combustion method using a very lean air/fuel mixture with a motor generator is advantageous because the energy density of the hydrogen-air mixture at lambda values over 2.00 is very low compared to the stoichiometry.
Keep in mind, Ford’s patent only covers methods of combustion and control of the hydrogen mixture. More work needs to be done to design machines capable of optimizing this method. The shape of the combustion chamber and the top of the piston has a significant effect on combustion, and both must be shaped to take advantage of hydrogen’s unique combustion properties.
Most promising however, hydrogen can take advantage of its very large bore-to-stroke ratio because unburned hydrocarbons are not a concern, parasitic losses are also reduced by using a short-stroke design. This means engines capable of screaming up to 20,000 rpm could be possible at the typical grocery store, reversing the current trend of characterless under square engines.