An engine system is provided, including a controller which estimates a mass ratio (G/F) of intake air inside a cylinder (containing fresh air and burnt gas) to fuel, and controls devices of an engine at a given engine speed so that, while a demanded engine load is a first load, at least part of a mixture gas inside the cylinder combusts by flame-propagation when the estimated G/F is below a first G/F, and the entire mixture gas combusts by compression ignition when the estimated G/F is above the first G/F, whereas while the demanded load is a second load (>the first load), at least part of the mixture gas combusts by flame-propagation when the estimated G/F is below a second G/F (<the first G/F), and the entire mixture gas combusts by compression ignition when the estimated G/F is above the second G/F.

The disclosure concerns a method for vibration reduction in a compression ignition four- stroke internal combustion engine. The internal combustion engine comprises exhaust and intake valves controlled by exhaust and intake camshafts. The method comprises, when operating the internal combustion engine below a threshold rotational speed, steps of: changing a timing of the exhaust camshaft to advance closing of the exhaust valve, and - changing a timing of the intake camshaft to delay opening of the intake valve.

The disclosure concerns a method for vibration reduction in a compression ignition four- stroke internal combustion engine. The internal combustion engine comprises exhaust and intake valves controlled by exhaust and intake camshafts. The method comprises, when operating the internal combustion engine below a threshold rotational speed, steps of: changing a timing of the exhaust camshaft to advance closing of the exhaust valve, and - changing a timing of the intake camshaft to delay opening of the intake valve.

Some embodiments described herein relate to a method of operating a compression ignition engine. The method of operating the compression ignition engine includes opening an intake valve to draw a volume of air into a combustion chamber, closing an intake valve, and moving a piston from a bottom-dead-center (BDC) position to a top-dead-center (TDC) position in the combustion chamber at a compression ratio of at least about 15:1. The method further includes injecting a volume of fuel into the combustion chamber at an engine crank angle between about 330 degrees and about 365 degrees during a first time period. The fuel has a cetane number less than about 40. The method further includes combusting substantially all of the volume of fuel. In some embodiments, a delay between injecting the volume of fuel into the combustion chamber and initiation of combustion is less than about 2 ms.

Some embodiments described herein relate to a method of operating a compression ignition engine. The method of operating the compression ignition engine includes opening an intake valve to draw a volume of air into a combustion chamber, closing an intake valve, and moving a piston from a bottom-dead-center (BDC) position to a top-dead-center (TDC) position in the combustion chamber at a compression ratio of at least about 15:1. The method further includes injecting a volume of fuel into the combustion chamber at an engine crank angle between about 330 degrees and about 365 degrees during a first time period. The fuel has a cetane number less than about 40. The method further includes combusting substantially all of the volume of fuel. In some embodiments, a delay between injecting the volume of fuel into the combustion chamber and initiation of combustion is less than about 2 ms.

A method for operating an internal combustion engine includes moving a piston downward from a top dead center position to a bottom dead center position expanding a combustion chamber in an intake stroke, dispensing a first portion of fuel into the combustion chamber, subsequent to moving the piston downward in the intake stroke, moving the piston upward in the vertical direction compressing the combustion chamber in a compression stroke, subsequent to moving the piston upward in the compression stroke, moving the piston downward in the vertical direction in an expansion stroke, while moving the piston downward in the vertical direction in the expansion stroke, dispensing a second portion of fuel into the combustion chamber, and while moving the piston downward in the expansion stroke, igniting at least a part of the first portion of fuel and the second portion of fuel.

A method for operating an internal combustion engine includes moving a piston downward from a top dead center position to a bottom dead center position expanding a combustion chamber in an intake stroke, dispensing a first portion of fuel into the combustion chamber, subsequent to moving the piston downward in the intake stroke, moving the piston upward in the vertical direction compressing the combustion chamber in a compression stroke, subsequent to moving the piston upward in the compression stroke, moving the piston downward in the vertical direction in an expansion stroke, while moving the piston downward in the vertical direction in the expansion stroke, dispensing a second portion of fuel into the combustion chamber, and while moving the piston downward in the expansion stroke, igniting at least a part of the first portion of fuel and the second portion of fuel.

An engine system is provided, including a controller which estimates a mass ratio (G/F) of intake air inside a cylinder (containing fresh air and burnt gas) to fuel, and controls devices of an engine at a given engine speed so that, while a demanded engine load is a first load, at least part of a mixture gas inside the cylinder combusts by flame-propagation when the estimated G/F is below a first G/F, and the entire mixture gas combusts by compression ignition when the estimated G/F is above the first G/F, whereas while the demanded load is a second load (>the first load), at least part of the mixture gas combusts by flame-propagation when the estimated G/F is below a second G/F (<the first G/F), and the entire mixture gas combusts by compression ignition when the estimated G/F is above the second G/F.

An engine system is provided, including a controller which estimates a mass ratio (G/F) of intake air inside a cylinder (containing fresh air and burnt gas) to fuel, and controls devices of an engine at a given engine speed so that, while a demanded engine load is a first load, at least part of a mixture gas inside the cylinder combusts by flame-propagation when the estimated G/F is below a first G/F, and the entire mixture gas combusts by compression ignition when the estimated G/F is above the first G/F, whereas while the demanded load is a second load (>the first load), at least part of the mixture gas combusts by flame-propagation when the estimated G/F is below a second G/F (<the first G/F), and the entire mixture gas combusts by compression ignition when the estimated G/F is above the second G/F.

Methods of operation of liquid and gaseous multi-fuel compression ignition engines that may be operated on a gaseous fuel or a liquid fuel, or a combination of both a gaseous fuel and a liquid fuel at the same time and in some embodiments, in the same combustion event. Various embodiments are disclosed.