Patent Description:
Conventional internal combustion engines using the Diesel or Otto cycle typically perform both the compression and the combustion/expansion in the same cylinder. However, split cycle internal combustion engines perform the compression and combustion/expansion stages in different cylinders. In such engines a fluid may be injected into the compression cylinder whilst air is being compressed. This has the effect of absorbing some of the heat produced during the compression stroke so that the compression may be considered at least quasi-isothermal.

<CIT> discloses a split cycle reciprocating piston engine configured to inject liquid nitrogen into a compression cylinder to act as a coolant. <CIT> discloses a liquid cleaning arrangement. <CIT> discloses a remote control device for intercepting naptha, oil and water filters, particularly for the naval, industrial and automotive sector.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:.

<FIG> shows a split cycle internal combustion engine apparatus <NUM> configured to use two different types of liquid coolant. The two liquid coolants may be selected so that they have different thermal properties, and so that combinations of the two liquid coolants may be used which provide improved engine performance. At least one of the liquid coolants may have been condensed into its liquid phase via a refrigeration process. The engine includes a controller which in operation receives an indication of at least one parameter of the engine, and uses this indication to control the delivery of at least one of the liquid coolants to a compression cylinder of a split-cycle engine in liquid form (for example, via direct injection) such that the liquid coolant vaporises into its gaseous phase during a compression stroke and a rise in temperature caused by the compression stroke is limited by the absorption of heat by the coolant. The controller may therefore be configured to deliver a combination of coolants that can be selected, for example, based on the demands of the engine. For example, the at least one liquid coolant is selected so that a phase change of the liquid coolant limits a rise in temperature caused by the compression stroke, for example the latent heat of vaporisation of the liquid coolant as it vaporises. Advantageously this may allow for a greater mass of air per compression stroke and therefore a more efficient engine. A more efficient engine has a clear environmental benefit.

<FIG> shows a split cycle internal combustion engine apparatus <NUM> comprising a compression cylinder <NUM> and a combustion cylinder <NUM>. The compression cylinder <NUM> accommodates a compression piston <NUM>, which is connected via a connecting rod <NUM> to a respective crank on a portion of a crank shaft <NUM>. The combustion cylinder <NUM> accommodates a combustion piston <NUM>, which is coupled via a connecting rod <NUM> to a respective crank on a portion of the crank shaft <NUM>. The compression cylinder <NUM> is coupled to the combustion cylinder <NUM> via a recuperator <NUM>. The compression cylinder <NUM> comprises an inlet port <NUM> for receiving air from outside the engine, and an outlet port <NUM> coupled to the recuperator <NUM>. The outlet port <NUM> comprises a non-return valve so that compressed air cannot flow back into the compression cylinder <NUM>. The combustion cylinder <NUM> comprises an inlet port <NUM>, which is also coupled to the recuperator <NUM>, and an outlet port <NUM> for passing exhaust from the combustion cylinder <NUM> to an exhaust <NUM>. These couplings provide an air flow path for air between the compression cylinder <NUM> and the combustion cylinder <NUM> via the recuperator <NUM>.

The engine <NUM> also comprises a first liquid coolant reservoir <NUM>, a second liquid coolant reservoir <NUM>, a controller <NUM> and a fuel reservoir <NUM>. The first liquid coolant reservoir <NUM> is coupled to the compression cylinder <NUM> via a first injector <NUM> thereby defining a first liquid flow path, and the second liquid coolant reservoir <NUM> is coupled to the compression cylinder <NUM> via a second injector <NUM> thereby defining a second liquid flow path. The fuel reservoir <NUM> is coupled to the combustion cylinder <NUM> via a third injector <NUM> so that a fluid flow path is defined between the fuel reservoir <NUM> and the combustion cylinder <NUM>.

The engine <NUM> comprises a plurality of sensors illustrated as black dots coupled to a controller <NUM>. However, it is to be appreciated that the sensors illustrated are only exemplary and there could be a different number of sensors or they could be placed in different locations. For example, the inlet port <NUM> may also comprise a temperature sensor. The sensors could be coupled to the controller <NUM> through physical wires or could be connected wirelessly. In the example shown in <FIG> there is a compression sensor <NUM> within the compression cylinder <NUM>. The sensor may for example be mounted proximate to the air inlet port <NUM> or proximate to one or both of the injectors <NUM>, <NUM>. The example engine <NUM> shown in <FIG> also comprises a combustion sensor <NUM> within the combustion cylinder <NUM>, and a recuperator sensor <NUM> within the recuperator <NUM>. Additionally, the engine <NUM> comprises a crank sensor <NUM> mounted to the crankshaft <NUM>, and an exhaust sensor <NUM> downstream of the outlet port <NUM> of the combustion cylinder <NUM>. In some examples, the first and second liquid coolant reservoirs <NUM>, <NUM> also comprise respective sensors, for example, for measuring a quantity, such as mass, of liquid contained in the reservoirs <NUM>, <NUM>.

The controller <NUM> is coupled to the sensors and at least one of the first and second injectors <NUM>, <NUM>. In the example shown in <FIG>, the controller <NUM> is coupled to both the first and second injectors <NUM>, <NUM>, as well as the third injector <NUM>.

The sensors are configured to send at least one signal to the controller <NUM> providing an indication of at least one parameter associated with the engine <NUM>. For example, in the example shown in <FIG>, the compression sensor <NUM> is configured to measure at least one parameter associated with the compression cylinder <NUM>. The combustion sensor <NUM> is configured to measure at least one parameter associated with the combustion cylinder <NUM>. The recuperator sensor <NUM> is configured to measure at least one parameter associated with the recuperator <NUM>. Additionally, the crank sensor <NUM> is configured to measure RPM for the engine, and the exhaust sensor <NUM> is configured to measure at least one parameter of exhaust gas expelled through the outlet port <NUM> of combustion cylinder <NUM>.

The engine <NUM> is arranged such that air is drawn into the compression cylinder <NUM> through the inlet port <NUM> of the compression cylinder <NUM>. The compression piston <NUM> is arranged to compress this air, and during the compression phase, liquid coolant is added into the compression cylinder <NUM>. The recuperator <NUM> is arranged to receive the compressed air via the outlet port <NUM> and pass it into the combustion cylinder <NUM> via inlet port <NUM>. The engine <NUM> is further arranged to add fuel from the fuel reservoir <NUM> to the compressed air in the combustion cylinder <NUM> via the third injector <NUM>, and combust the mixture of fuel and compressed air (for example via operation of an ignition source, not shown) to extract useful work via turning of the crankshaft <NUM>.

The fuel reservoir <NUM> is connected to the controller <NUM> so that the controller <NUM> controls the delivery of fuel into the combustion cylinder <NUM>. In some examples, the controller <NUM> is configured to determine the amount of fuel to be injected based on the indication of the at least one parameter of the engine <NUM>. For example the controller <NUM> may be configured to obtain the indication of the at least one parameter via a signal received from the exhaust sensor <NUM>.

Each of the sensors are configured to send a respective signal to the controller <NUM>, and the controller <NUM> is configured to make a determination for controlling delivery of at least one of the first liquid coolant and the second liquid coolant based on these received signals. The controller <NUM> is configured to control delivery of at least one of the first and second coolants respectively such that the liquid coolant vaporises into its gaseous phase during a compression stroke of the compression piston <NUM> and a rise in temperature caused by the compression stroke is limited by the absorption of heat by the liquid coolant. For example, the controller <NUM> is operable to control the timing of the first and second injectors <NUM>, <NUM> to dispense liquid into the compression cylinder <NUM> based on the position of the compression piston <NUM> in the compression cylinder <NUM>, for example as determined by a crank angle measured by the crank sensor <NUM>. In some examples the controller <NUM> may additionally or alternatively be configured to operate one or more pumps in each of the respective liquid reservoirs <NUM>, <NUM>, to control delivery of at least one of the liquid coolants to the compression cylinder <NUM>.

The controller <NUM> and the injectors <NUM>, <NUM> are configured to inject the liquid coolant directly into the compression cylinder <NUM> at a low pressure, for example less than <NUM> MPa, for example less than <NUM> MPa, for example less than <NUM> MPa, for example less than <NUM> MPa, for example less than <NUM> MPa. This may have the advantage of not requiring a specialist cryogenic pump for pumping the liquid coolant into the compression cylinder <NUM>. The liquid coolant can be injected directly into the compression cylinder <NUM> in the liquid phase and in the form of a spray of droplets but with a large distribution in droplet sizes. Having a large distribution in droplet sizes is thermodynamically favourable because it spreads out the temperature and/or time range over which the liquid coolant vaporises into the gaseous phase during the compression stroke of the compression piston <NUM>.

The first liquid coolant may be a liquid coolant which has been condensed into a liquid phase via refrigeration. For example, the first liquid coolant may be a cryogenic liquid such as liquid nitrogen (LN<NUM>). The second liquid coolant may be water. It will be understood, however, that any other non-oxidising, non-combustible liquefied gas may be used as the first and/or second liquid coolants, for example a gas that has been liquefied via a refrigeration process, such as air, oxygen or argon. The fuel may be a fuel that requires a source of ignition (for example the ignition source may comprise spark plugs in the combustion cylinder) such as gasoline, hydrogen, liquefied natural gas, and compressed natural gas. Alternatively the fuel may be a fuel which does not require a source of ignition, for example, it may be a compression-ignited fuel such as diesel.

The controller <NUM> is configured to determine the delivery requirements for at least one of the liquid coolants and to control the injectors to meet said delivery requirements. The delivery requirements may, for example, be based on current operating conditions of the engine <NUM> (such as load or operating temperature) or may be based on the amount of liquid coolant in each of the respective reservoirs <NUM>, <NUM>, so that resources may be conserved. The controller <NUM> is configured to determine the delivery requirements in response to receiving an indication of at least one parameter associated with the engine <NUM>. For example, the controller <NUM> may comprise at least one lookup table (LUT), and may be configured to determine a delivery requirement based on a received signal comprising at least one data value from a sensor and based on a comparison of that received data value in the lookup table. Receiving the indication may be in the form of receiving feedback such as a signal from one or more of the plurality of sensors. It is to be appreciated in the context of this disclosure a variety of parameters of the engine may be monitored by the controller <NUM>. Such parameters may include parameters relating to the compression cylinder <NUM>, such as temperature, pressure or saturation of liquid coolant, and may be measured in a number of places throughout the engine <NUM>.

In some examples, the compression sensor <NUM> is configured to measure pressure and/or temperature in the compression cylinder <NUM>, the combustion sensor <NUM> is configured to measure pressure and/or temperature in the combustion cylinder <NUM> and the recuperator sensor <NUM> is configured to measure the oxygen concentration level, the water saturation level, pressure and temperature in the recuperator. Additionally, the crank sensor <NUM> is configured to measure an RPM for the crankshaft <NUM> and the exhaust sensor <NUM> is configured to measure pressure and/or temperature of the exhaust, and/or the composition of the exhaust, for example the concentration of carbon dioxide, nitrogen dioxide, or other gases or particulates in the exhaust. There may be a number of other inputs for the controller <NUM>, such as a current operating RPM of the compression cylinder <NUM> and/or the combustion cylinder <NUM>. Likewise, the controller <NUM> may be configured to receive a demand signal representative of the current levels of demand for the engine, or any other indication which may have an effect on the way in which the liquid coolant and/or fuel could be used.

In operation, air is drawn into the compression cylinder <NUM> through the inlet port <NUM> of the compression cylinder <NUM> via movement of the compression piston <NUM> downward through the compression cylinder <NUM> by rotation of the crankshaft <NUM> until the compression piston <NUM> reaches bottom dead centre (BDC). The crankshaft <NUM> continues to rotate and pushes the compression piston back up from BDC towards top dead centre (TDC). As the compression piston <NUM> travels upwards toward TDC, the compression piston <NUM> compresses this air. The controller <NUM> receives indications of at least one parameter of the engine <NUM> from sensors in the engine <NUM>, and in response, controls delivery of at least one of the liquid coolants during the compression phase by injecting the at least one liquid coolant into the compression cylinder <NUM> in a liquid phase, for example in the form of a liquid spray via injectors <NUM>, <NUM>. As the compression piston <NUM> continues to move towards TDC, the injected liquid coolant vaporises into a gaseous phase and the latent heat of vaporisation at least partially limits a rise in temperature of the air in the compression cylinder <NUM> due to its compression.

The recuperator <NUM> then receives the compressed fluid (comprising the vaporised liquid coolant) from the compression cylinder <NUM> via the outlet port <NUM> and passes it into the combustion cylinder <NUM> via inlet port <NUM>. In the process, the recuperator <NUM> heats the compressed air to a desired temperature, for example to aid the combustion process in the combustion cylinder <NUM>. The controller then operates the third injector <NUM> to deliver fuel to the compressed air in the combustion cylinder <NUM>, and combusts the mixture of fuel and compressed air and vaporised liquid coolant (for example by operating an ignition source such as a spark plug, not shown) to extract useful work via turning of the crankshaft <NUM>.

Several examples will now be discussed below where the controller <NUM> receives an indication at least one parameter of the engine <NUM> and, in response to receiving said at least one indication, the controller <NUM> controls the delivery of at least one liquid coolant to the compression cylinder <NUM>.

In a first example, the first coolant is a liquid that has been liquefied via a refrigeration process, such as liquid nitrogen, and the second coolant is water, and the at least one parameter is a water saturation level. The water saturation level is detected based on measuring the temperature and pressure of the air entering into the compression cylinder <NUM> via the inlet port <NUM>. Using the pressure and temperature of the air in the compression cylinder <NUM> (which of course has a known volume depending on the location of the compression piston <NUM>, which can be determined by a crank angle as measured by sensor <NUM>), a number of moles of air contained within the compression cylinder <NUM> may be determined. Using Dalton's law of partial pressures, the pressure of the added medium is proportional to the molar concentration. Accordingly, the controller <NUM> can determine whether or not the water will boil (based on known values of pressure-dependent boiling temperatures of water, for example stored in a look up table in the controller <NUM>), and by measuring the amount of water injected into the compression cylinder <NUM> via injector <NUM>, (for example using a flow meter) it is possible for the controller <NUM> to determine the water saturation level.

In response to determining the water saturation level of the compression cylinder <NUM>, the controller <NUM> may be configured determine a quantity of liquid coolant to inject and operate the injectors <NUM>, <NUM> to inject either liquid nitrogen and/or water based on the water saturation level. For example, the controller <NUM> may use water as the only coolant until the water saturation reaches a threshold level. Above this threshold level, only the second liquid coolant (liquid nitrogen) may be injected into the compression cylinder <NUM> and no water may be injected. Additionally or alternatively, the controller <NUM> may be configured to use a combination of water and liquid nitrogen to achieve a desired level of water saturation. For example, the controller <NUM> may be configured to adjust the ratio of the two liquid coolants injected into the compression cylinder <NUM> based on the water saturation level.

The controller <NUM> may comprise stored data, for example in the form of a lookup table, which defines the water saturation threshold. This threshold may be defined in a number of ways. However, it is preferable to reduce the amount of liquid water in the combustion cylinder <NUM>, such as having no liquid water in the combustion cylinder and only water in the form of water vapour in the combustion cylinder <NUM>. Accordingly, the water saturation threshold may be determined to be less than <NUM>% absolute humidity.

The controller <NUM> may be configured to determine the threshold based on other engine parameters, such as the volume of oxygen, the temperature or the pressure, as these parameters may affect the functioning of the engine and the boiling point of the water.

In a second example, the controller <NUM> may be configured to determine the temperature in the compression cylinder <NUM> based on an indication received via a signal from the compression sensor <NUM>. In response to the controller <NUM> determining a temperature in the compression cylinder <NUM> being below a threshold value based on an indication received from the compression sensor <NUM>, the controller <NUM> is configured to reduce the delivery of both a first liquid coolant and a second liquid coolant to the compression cylinder <NUM>. Such a situation may happen when the engine <NUM> is first started and is relatively cold. Conversely, the controller <NUM> may be configured to increase the delivery of the first and/or second liquid coolants to the compression cylinder <NUM> in response to determining that the temperature is above the threshold value, for example once the engine has warmed up and/or is placed under a high load demand or is running at a high RPM.

In some examples, the controller <NUM> is configured to compare a current temperature value and a threshold value, and make a determination based on that comparison. For example, the controller <NUM> is configured to make a determination to control the delivery (for example in terms of mass) of at least one of the first liquid coolant and the second liquid coolant based on a comparison of the current temperature value with a threshold value. For example, the controller <NUM> is configured to control delivery of at least one of the first liquid coolant and the second liquid coolant in proportion to the difference from the threshold value, so that a greater or lesser quantity (for example mass) of liquid coolant is delivered based on the greater the difference from the threshold value.

The extent to which the delivery of the first and/or second liquid coolants changes may be proportional to a temperature difference between a temperature inside the compression cylinder <NUM> (for example as measured by the compression sensor <NUM>) and a threshold temperature (for example as stored in the controller <NUM>). In response to determining that the delivery of a liquid coolant to the compression cylinder should be increased, the controller <NUM> may only use one of the liquid coolants (such as water) as the liquid coolant until a (water) saturation threshold is reached. A similar approach may be adopted for other parameters of the engine, such as a pressure in the compression cylinder <NUM>.

In a third example, the controller <NUM> is configured to determine an oxygen saturation level in the recuperator <NUM> based on an indication of a parameter received via a signal from the recuperator sensor <NUM>. The controller <NUM> is configured so that if the oxygen saturation is above a threshold level, more liquid coolant is injected into the compression cylinder <NUM>. The injection of liquid coolant may be in accordance with the approach described above.

In a fourth example, the controller <NUM> is configured to control the delivery of at least one of the liquid coolants based on a demand placed on the engine <NUM>. For example, the controller <NUM> is configured to receive a signal indicating a desired output from the engine (for example, a desired torque, RPM or power output). In this example the first liquid coolant is a liquid that has been liquefied via a refrigeration process, such as liquid nitrogen, and the second liquid coolant is water. The controller <NUM> is configured to controller the delivery of the first liquid coolant and the second liquid coolant so that at a high demand (when the engine will be running hotter) more of the first liquid coolant is injected into the compression cylinder <NUM> relative to the second liquid coolant, but at a low demand (when the engine will be running cooler) the controller <NUM> is configured to inject more of the second liquid coolant relative to the first liquid coolant. In this way, the temperature of the compressed air in the compression cylinder <NUM> can be more accurately controlled to enable more efficient combustion and thereby a more efficient engine <NUM>.

In some examples, the injectors <NUM>, <NUM>, <NUM> may also be configured to act as sensors and send a signal providing an indication of at least one parameter associated with the engine <NUM> to the controller <NUM>. The injectors <NUM>, <NUM>, <NUM> may be configured to send a signal indicating, for example, at least one of the temperature of the injector, a resistance of a component of the injector (such as induction coils operable to cause the injector to inject a liquid) and/or a measurement indicating the amount (such as mass) of liquid injected via that injector <NUM>, <NUM>, <NUM>. The injectors may be configured to inject the liquid coolant by direct injection and/or common rail injection, however, due to the low temperatures that may be involved, at least one injector <NUM>, <NUM>, <NUM> may not comprise a piezoelectric driving element but may be configured to operate at low temperatures, such as less than <NUM> Kelvin.

In some examples, the controller <NUM> is configured to determine and control the rate of delivery of one liquid coolant with respect to another liquid coolant. For example, the controller <NUM> may comprise a number of open or closed control loops to control the ratio of coolants injected into the compression cylinder <NUM>. These feedback loops may include measurements of the temperature of the exhaust gases, the load of the engine, a desired level of differential temperatures and the density of the fluid. For example, the controller <NUM> may be a proportionalintegral-derivative (PID) controller. In the example shown in <FIG>, the controller <NUM> controls the ratio of the first liquid coolant to the second liquid coolant. Alternatively, the controller <NUM> may be configured to focus primarily on one coolant, and only use the other coolant in certain situations, such as when a threshold value is reached. This may help to conserve resources, for example when one of the liquid coolants is running low. In such an example, the controller <NUM> may retain the injection quantity of one coolant at a selected value, and in response to the controller <NUM> determining that more liquid coolant should be added to the compression cylinder <NUM>, it is configured to add liquid coolant only from the same liquid coolant reservoir, until the threshold condition is reached. Once the threshold is reached, the controller <NUM> may be configured to switch so that only liquid coolant from the other reservoir is added.

In some examples, the injection of the spray of droplets by injectors <NUM>, <NUM> is controlled (for example by the controller <NUM>) to deliver a distribution of droplet sizes to provide steady heat absorption during the compression stroke, and a smooth heat transfer between the air in the cylinder <NUM> and the liquid coolant. In some examples, this will comprise determining (for example, by the controller <NUM>) the distribution of droplet sizes that will provide heat absorption throughout the compression stroke, for example throughout a portion of the compression stroke or throughout the entire compression stroke (from BDC to TDC, for example). In the case of the liquid coolant being one that has been liquefied via a refrigeration process, the combination of the low temperature of the liquid coolant and the low pressure at which it is injected means that the liquid coolant is injected into the compression cylinder <NUM> in the liquid phase even when the temperature of the engine is high.

In some examples the liquid coolant is injected into the compression cylinder <NUM> in the form of a liquid flow. In some examples, the controller <NUM> is configured to control the rate of delivery of at least one of the liquid coolants such that the absorption of heat by the liquid coolant is commensurate with the instantaneous temperature difference between the liquid coolant and surrounding air in the cylinder <NUM>.

In some examples, the inlet port <NUM> may be coupled to a turbocharger or any other forced induction device, such that the air entering the compression cylinder <NUM> has been charged. In some examples, the inlet port <NUM> may additionally or alternatively be coupled to an intercooler to cool the charged air. Charging and cooling the air in this way may also mean that a measurement of the pressure and temperature of air entering the compression cylinder <NUM> via inlet port <NUM> can be more accurately determined.

In some examples, the engine <NUM> may comprise a third liquid coolant reservoir and another liquid coolant injector coupled to third liquid coolant reservoir, and arranged to inject the third liquid coolant into a part of the engine <NUM>, such as the compression cylinder <NUM> or recuperator <NUM>. The third liquid coolant may be different to the first and second liquid coolants, and may be a non-oxidising, non-combustible gas, for example that has been liquefied into a liquid phase via a refrigeration process.

In some examples, the recuperator <NUM> may comprise an injector coupled to a liquid coolant reservoir. For example, the recuperator <NUM> may also comprise an injector coupled to the second liquid coolant reservoir and the controller <NUM> may be configured to monitor a temperature of the compressed fluid passing from the compression cylinder <NUM> to the combustion cylinder <NUM>, for example via recuperator sensor <NUM>. The controller <NUM> may be configured to determine if a quantity of liquid coolant is required in order to control the temperature of the gas entering the combustion cylinder <NUM> via inlet port <NUM> to be within a selected range. The selected range may be chosen to achieve efficient combustion and may be stored in a memory of the controller <NUM>. For example, if the engine <NUM> is being run hard, for example because a high demand is placed on it, the injection of the first and second liquid coolants into the compression cylinder <NUM> may not be enough to keep the temperature of the compressed air passing from the compression cylinder <NUM> to the combustion cylinder <NUM> to be within the selected range, and so the controller <NUM> may be configured to control the delivery of liquid coolant into the recuperator <NUM> via operation of the injector to further cool the air to be within the selected range.

In some examples, the controller <NUM> may be configured to deliver liquid air to the compression cylinder <NUM> to improve the combustion efficiency of the engine <NUM>, or for example, when a high demand is placed on the engine <NUM>.

<FIG> shows another example of a split cycle combustion engine apparatus <NUM>. The same reference numerals have been used where they relate to the same or a similar feature as in <FIG>.

The engine <NUM> of <FIG> differs from the engine <NUM> of <FIG> in that in the engine <NUM> of <FIG> the second liquid coolant reservoir <NUM> is coupled to the recuperator <NUM>. The controller <NUM> is configured to control delivery of liquid coolant from the second liquid coolant reservoir <NUM> so that the second liquid coolant may be injected into the recuperator <NUM> as well as the compression cylinder <NUM>. The crankshaft <NUM> also includes a gearing mechanism <NUM> configured so that the compression piston <NUM> and the combustion piston <NUM> may operate at a different RPM.

Additionally, the engine <NUM> is configured so that exhaust air from the combustion cylinder <NUM> passes through the outlet port <NUM> and is routed back through the recuperator <NUM> so that the exhaust gas is in a heat exchange relationship with the compressed air entering the combustion cylinder <NUM>. In this way, the temperature of the gas passing from the compression cylinder <NUM> to the combustion cylinder <NUM> may be controlled so that the engine is operating at a more efficient operating temperature.

In addition, the recuperator <NUM> comprises a condenser so that some of the second liquid coolant may be extracted from the exhaust air and returned to the second liquid coolant reservoir <NUM>. The exhaust air may then be expelled from the recuperator <NUM> to the environment via exhaust <NUM>. In the example shown in <FIG>, the engine <NUM> also comprises an expulsion sensor <NUM> connected to the controller <NUM>, for example located in the exhaust flow path downstream of the recuperator <NUM>. The expulsion sensor <NUM> may be configured to measure the concentration of gasses and/or particulates leaving via exhaust <NUM> and send a signal comprising an indication of one of these parameters to the controller <NUM>.

Another difference from the engine <NUM> of <FIG> is that the two portions of the crankshaft <NUM> to which the two pistons <NUM>, <NUM> are respectively attached via connecting rods <NUM>, <NUM> are not integrally connected together to rotate at the same speed. Instead, the two portions are connected via a gearing mechanism <NUM> which may be, for example, a transmission system or gear box of selectively variable transmission ratio. Additionally or alternatively, the gearing mechanism <NUM> may comprise a clutch such as a disconnect clutch.

The operation of the engine <NUM> of <FIG> is much the same as the operation described above for the engine <NUM> of <FIG>. However, the operation of previously undescribed features of the engine <NUM> will now be described with reference to <FIG>.

The condenser in the recuperator <NUM> is configured to cool the exhaust air from the combustion chamber <NUM>. For example, where the second liquid coolant is water, this water may be cooled and condensed so that it is returned to the second liquid coolant reservoir <NUM>, which allows for the provision of a smaller second liquid coolant reservoir <NUM>. This may be preferable when using the engine on an automobile which does not have unlimited access to water, and thus water recycling may be used. The excess heat from the exhausted air may also be used to provide a heating mechanism for the air in the recuperator, such as a heat exchanger in heat exchange relationship with compressed air expelled from the compression cylinder <NUM> and entering the combustion cylinder <NUM>. For example, the controller <NUM> may be configured to control operation of the recuperator <NUM> so that the compressed air passing from the compression cylinder <NUM> to the combustion cylinder <NUM> is within a selected range. For example, the controller <NUM> may be configured to heat the air if it is below the selected threshold (for example if the engine <NUM> is running cold, for example if it has just started), and it may be configured to cool the air if it is above the selected threshold (for example a high demand is placed on the engine <NUM>). The controller <NUM> may cool the air in the recuperator may controlling the delivery of the second liquid coolant from the second liquid coolant reservoir <NUM>, for example via operation of an injector in the recuperator <NUM>.

In some examples, the engine <NUM> may also include a turbo charger or other suitable device for improving engine efficiency by extracting energy from the exhaust gas of the combustion cylinder <NUM>.

In some examples, the engine <NUM> may also include a supercharger or other suitable device for increasing the pressure or density of the air supplied to the engine <NUM>. Power for the supercharger may be provided by the crankshaft, a battery or any other suitable means.

In some examples, the engine <NUM>, <NUM> may comprise a liquid nitrogen generator of known Brayton/Joule/Thompson type. This generator may include a rotary compressor, whose shaft is connected to a turbine expander and to the output of a variable ratio transmission system, the input of which is connected to the crankshaft <NUM>. The liquid nitrogen generator also includes two heat exchangers and a fan-cooled aftercooler. In use, air is drawn into the liquid nitrogen generator by the compressor through an inlet and after compression, expansion and passing through the heat exchangers, liquid nitrogen is generated and passed to the reservoir <NUM>.

A method of determining the amount of coolant to be used will now be described with reference to <FIG>.

In <FIG>, at step <NUM>, the process begins. Steps <NUM> and <NUM> respectively comprise determining the demand and the RPM for the engine, so that at step <NUM>, the controller <NUM> is configured to calculate the required amount of fuel to be injected from the fuel reservoir <NUM> into the combustion cylinder <NUM>. At step <NUM>, the controller <NUM> uses the measured conditions of the compressed air delivered from the compression cylinder <NUM> to the combustion cylinder <NUM>, i.e. based on received signals from the compression sensor <NUM> and recuperator sensor <NUM>, so that at step <NUM> the controller <NUM> determines the oxygen mass required for the desired combustion effect. At step <NUM>, the maximum mass of the coolants is determined. In this case, the first liquid coolant is the liquid nitrogen and the second is water.

At step <NUM>, the controller determines, based on an indication from one of the sensors, whether or not the oxygen level is above a threshold value by comparing a data value based on the received sensor signal with a stored lookup table. If the oxygen level is determined to be above the threshold value then the method proceeds to step <NUM> where the controller <NUM> is configured to determine if a water saturation threshold has been reached. However, if the oxygen level is below the threshold value then the method proceeds to step <NUM>, where the controller <NUM> is configured to reduce the amount of water and liquid nitrogen added to the compression cylinder.

The controller <NUM> may be configured to determine the oxygen mass required based on the fuel load, for instance using a lookup table comprising known oxygen requirements for the desired combustion based on the thermodynamic properties of the engine. In some embodiments, there may be more than one source of oxygen present, for example, oxygen in the air and oxygen in the form of liquid oxygen/liquid air being injected into the compression cylinder <NUM> as liquid coolants. Accordingly, the controller <NUM> is configured to determine the oxygen level in the engine, and it may adjust the quantities of liquid coolant injected into the compression cylinder <NUM> to ensure the oxygen level remains within a selected range.

The controller <NUM> may be configured to determine the oxygen level using one of the sensors. A lambda meter (an oxygen sensor) may be used to measure the oxygen concentration, for example in the recuperator <NUM>. It is preferable to ensure that the oxygen levels do not get too low as this may result in soot building up in the exhaust and slip in the combustion cylinder.

At step <NUM>, the water saturation level is determined by the controller, for example based on an indication from one of the sensors. If the water saturation level has reached a selected water saturation threshold then the method proceeds to step <NUM>, where the controller <NUM> is configured to increase the amount of liquid nitrogen to be injected into the compression cylinder <NUM>. At this stage, the controller <NUM> may refrain from injecting any more water into the compression cylinder <NUM> until the water saturation level if below the water saturation threshold value. If, at step <NUM>, the water saturation level is below the water saturation threshold then the method proceeds to step <NUM>, where the controller <NUM> is configured to increase the amount of water injected into the compression cylinder <NUM>. At this stage, the controller <NUM> may refrain from injecting any liquid nitrogen into the compression cylinder <NUM> until the water saturation threshold is reached.

After both steps <NUM>, <NUM> and <NUM>, the method proceeds to step <NUM>. Step <NUM> draws input from step <NUM>, where the heat in the exhaust is measured, for example using one of the exhaust sensor <NUM> or the expulsion sensor <NUM>. At step <NUM>, the controller <NUM> is configured to measure at least one of: temperature, pressure and oxygen content in the recuperator <NUM>. For instance, this may be determined using the recuperator sensor <NUM>. Step <NUM> may commence a cycle of measuring the temperature, pressure, oxygen saturation and water saturation and the controller <NUM> receiving signals based on these measured parameters, and adjusting the delivery of coolant accordingly.

At step <NUM>, the controller <NUM> is configured to determine, based on a temperature measurement from one of the sensors, whether the temperature in the compression cylinder <NUM> is above a threshold value. If the temperature is high enough, for example above the threshold value, the method proceeds to step <NUM>, where the controller <NUM> is configured to determine whether the pressure in the compression cylinder <NUM> is above a threshold value. If the pressure is high enough, for example above the threshold value, the method proceeds to step <NUM>, as discussed above. For any of steps <NUM>, <NUM> and <NUM>, if the threshold values are not reached, the method proceeds to step <NUM>, where the controller <NUM> is configured to reduce the amount of both of the liquid coolants delivered.

<FIG> shows a liquid coolant injection apparatus <NUM> for injecting a liquid coolant into the compression cylinder <NUM> of a split cycle engine, such as the engine <NUM>, <NUM> described above. The apparatus <NUM> is operated by a controller such as controller <NUM> described above, which may be configured to control delivery of at least one of a first liquid coolant and a second liquid coolant based on an indication of at least one parameter associated with the engine <NUM>, <NUM>.

The coolant injection apparatus <NUM> shown in <FIG> comprises a liquid coolant reservoir <NUM> coupled to a compression cylinder <NUM> of a split cycle engine via a filter <NUM> and a liquid coolant injector <NUM>. The reservoir <NUM> is in fluid communication with a liquid coolant fluid path that extends through the filter <NUM> to the liquid coolant injector <NUM>. The liquid coolant injector <NUM> is coupled directly to the compression cylinder <NUM>.

The liquid coolant reservoir <NUM> is operable to provide a liquid coolant to the filter <NUM> via the liquid coolant flow path. The filter <NUM> is operable to remove solid contaminants from the liquid coolant and enable the flow of filtered liquid coolant to the liquid coolant injector <NUM> which is operable to control the injection of liquid coolant into the compression cylinder <NUM>.

The system of <FIG> will now be described in operation as an example. The reservoir <NUM> stores a liquid coolant, this could be liquefied air, water or another liquid that has been condensed into a liquid phase via refrigeration. In this example the liquid coolant is liquid nitrogen.

As shown in <FIG>, the reservoir <NUM> contains a driver that is able to increase the pressure within the reservoir <NUM>, thereby forcing the liquid nitrogen along the liquid coolant flow path. The driver may comprise a heater <NUM> and/or pump <NUM> which can produce a pressure differential between the reservoir <NUM> and the liquid coolant flow path <NUM>. For example, a heater <NUM> is operable to heat a portion of the reservoir <NUM> in response to a control signal from the controller <NUM>. This creates a pressure differential in the reservoir <NUM> to drive a portion of the liquid nitrogen towards the compression cylinder <NUM>. The heater <NUM> may recycle heat from the engine through the exhaust or may comprise a resistor that a potential difference is applied across to cause heating. In some examples, the reservoir <NUM> also comprises a pressure release valve to prevent over pressurisation of the reservoir <NUM>. This valve allows the nitrogen gas generated by the heater to vent in the case that the pressure of the tank <NUM> is beyond a selected threshold. This threshold may, for example, be based on an upper operating pressure of the liquid coolant injection system <NUM>, for example, as determined by the controller <NUM>. The provision of a heater <NUM> in the reservoir <NUM> may also act to prevent the reservoir <NUM> from achieving sub-atmospheric pressures, which is undesirable as sub-atmospheric pressures may draw ambient air into the reservoir <NUM> which may freeze and form undesirable ice crystals. Once a pressure differential has been achieved within the reservoir <NUM> using the methods and apparatus described above with reference to <FIG>, the liquid nitrogen flows towards the compression cylinder <NUM> due to the created pressure differential. The liquid coolant flow path passes through a filter <NUM> which removes solid contaminants from the liquid nitrogen. This filtering step helps to remove impurities within the nitrogen gas, such as water or carbon dioxide crystals, which can damage the liquid coolant injector <NUM> via abrasion.

After passing through the filter <NUM>, the liquid nitrogen continues along the liquid coolant flow path to the liquid coolant injector <NUM> due to the pressure differential. The injector <NUM> is operable, by a control signal from the controller <NUM>, to inject a determined amount of liquid nitrogen into the compression cylinder <NUM>. The delivery of the liquid nitrogen may be controlled by the controller <NUM> based on received parameters as described above in relation to <FIG>.

<FIG> shows a filter apparatus <NUM> according to the invention for removing solid contaminants from a cryogenic liquid coolant flow path, for example for use with the coolant injection apparatus <NUM> described above with respect to <FIG>. The filter <NUM> comprises two liquid coolant flow paths <NUM>, <NUM> coupled in parallel to an inlet <NUM> and an outlet <NUM> at respective ends thereof. The filter <NUM> comprises two portions <NUM>, <NUM> wherein one portion <NUM> lies along the first liquid coolant flow path <NUM> between the inlet <NUM> and the outlet <NUM> and a second filter portion <NUM> lies along a second liquid coolant flow path <NUM> between the inlet <NUM> and outlet <NUM>. The filter comprises at least one, optionally two diverters <NUM>, <NUM>, one on either side of the filter portions <NUM>, <NUM>, each diverter <NUM>, <NUM> at a respective join between the inlet <NUM> and the two flow paths <NUM>, <NUM> and the outlet <NUM> and the two flow paths <NUM>, <NUM>. Additionally, in the example shown in <FIG> there are two heating elements <NUM>, <NUM>, each coupled to a respective filter portion <NUM>, <NUM>. The heating elements <NUM>, <NUM> and diverters <NUM>, <NUM> are coupled to a controller <NUM>, which may be the same controller <NUM> as the controller described above in relation to <FIG>.

The diverters <NUM>, <NUM> are operable to direct the liquid coolant along the liquid coolant flow path and are controlled by the controller <NUM>. These diverters may be valves that modify the liquid coolant flow path and allow the filter portions <NUM>, <NUM> to be interchanged. The controller <NUM> may operate these diverters <NUM>, <NUM> according to a selected routine (for example as stored in the controller <NUM>), allowing each filter portion <NUM>, <NUM> to be in the liquid coolant flow path for a selected time interval before interchanging the filter portions <NUM>, <NUM>, for example so that liquid coolant flows through the first liquid flow path <NUM> for a first selected time interval, and then through the second liquid flow path <NUM> for a second selected time interval, and so on. Alternatively, the controller <NUM> may receive signals comprising sensor data that can be used to determine properties of the liquid coolant flow. For example, the filter apparatus <NUM> could include pressure sensors located along the liquid coolant flow path <NUM>, <NUM>, sensors in the inlet <NUM> and outlet <NUM>, and/or sensors in the reservoir <NUM>, and at the input of an injector coupled to the outlet <NUM> of the filter apparatus.

For example, the controller <NUM> may be configured to determine if a blockage exists in the filter portions <NUM>, <NUM> and operate the diverters <NUM>, <NUM> and heating elements <NUM>, <NUM> accordingly. For example, if the pressure difference between the input of the filter <NUM> and the input of the injector exceeds a selected threshold, this may indicate that the first filter portion <NUM> is close to saturation with solid contaminants and is providing a significant blockage in the liquid coolant flow path <NUM>. The controller <NUM> may therefore determine that a blockage condition exists, and control the diverters <NUM>, <NUM> to divert liquid away from the first liquid flow path <NUM> and only via the second liquid flow path <NUM> via second filter portion <NUM>. Because no liquid coolant is passing through the first liquid flow path <NUM> and through the first filter portion <NUM>, the first filter portion <NUM> can either heat naturally due to the ambient temperature (and because no cold liquid coolant is flowing through it), or it can be heated, for example by the controller <NUM> controlling the heating element <NUM>, to remove the solid contaminants by melting and/or evaporation. Once the solid contaminants have been removed, the diverters <NUM>, <NUM> may be operated to pass the liquid coolant back through both liquid flow paths <NUM>, <NUM> or through only one liquid flow path <NUM>, <NUM> at a time.

A further option may include sensing the temperature of the filter portions <NUM>, <NUM>. When the filter becomes "clogged" with containments the local temperature of the filter portions <NUM>, <NUM> may increase, indicating a clog condition. This can be sensed by a temperature sensor, such as a thermocouple, and reported to the controller <NUM> via sensor signals. The controller <NUM> may determine that the filter portions <NUM>, <NUM> should be interchanged based on these received sensor signals.

In some examples, the controller <NUM> may be configured to reduce the flow rate of liquid coolant through the filter <NUM> to create an increase in temperature of the filter portions <NUM>, <NUM>.

In the embodiment of <FIG>, the filter portions <NUM>, <NUM> are copper meshes capable of catching solid contaminants but allowing the passage of liquid coolant therethrough. The use of a copper mesh is advantageous as it is conductive, allowing the heaters <NUM>, <NUM> to be inductive coils that can be located outside of the liquid coolant flow path but still provide the desired heating effect. When the filter portions <NUM>, <NUM> are interchanged, the inactive portion may be "clogged", holding a large amount of solid contaminants. The heaters <NUM>, <NUM> allow the copper mesh to be heated, causing the solid contaminants to either evaporate or melt. These can then be vented from the filter <NUM> using a pressure release valve.

In addition to the use of heating to remove solid contaminants, the filter may comprise U-bends, for example in each liquid coolant flow path <NUM>, <NUM>,so as to inhibit any liquid that does not completely evaporate, such as water, from building up and being carried with the liquid coolant flow, thus potentially damaging the engine <NUM>, <NUM>. The U-bends may further comprise a valve arranged so that the U-bends can be drained at selected intervals, for example by operation of the controller <NUM> or by a user.

Alternative embodiments may use different heating means to those described above. These could include using recycled heat from the exhaust of the split cycle engine <NUM>-, <NUM> to heat the filter portions <NUM>, <NUM>. This has the advantage of not requiring an additional heating system and may be more efficient as it uses recovered heat. Depending on the heating of the surrounding apparatus, the filter portions <NUM>, <NUM> may not require active heating and instead they may simply be allowed to warm up to the ambient temperature, which may be sufficient to enable solid contaminants to be removed from the filter <NUM>.

In addition to different heating means, the material of the filter portions <NUM>, <NUM> can also be varied. For example, instead of copper in the above example, the filter portions <NUM>, <NUM> could comprise an aluminium mesh which could also be heated through inductive heating. Other materials such as carbon fibres may also be used.

<FIG> shows an alternative arrangement of the liquid coolant reservoirs described and shown in <FIG> for use with the split cycle engine apparatus of <FIG> and <FIG>. The reservoir <NUM>, <NUM> comprises an insulated tank <NUM> arranged to enclose a liquid coolant <NUM> such as a cryogen, for example liquid nitrogen, that has been condensed into a liquid phase via a refrigeration process. At the bottom of the tank <NUM> is a driver <NUM> arranged to create a pressure differential in the tank <NUM>, such as the driver described above in relation to <FIG>. In the example shown the driver <NUM> is a resistive element arranged to provide a degree of resistive heating to the liquid coolant when a current is passed through it. The tank <NUM> is coupled to a compression cylinder <NUM> of a split cycle engine <NUM>, such as the engine of <FIG> and <FIG>, via an insulated line <NUM> through filter <NUM> and injector <NUM>, as discussed above in relation to the earlier Figs.

The insulated line <NUM> extends through the wall of the tank <NUM> and extends down to the bottom of the tank <NUM> so that it can still extract liquid coolant even when the level of liquid coolant in the tank is low. It will be understood that the insulated line <NUM> need not be insulated inside the tank <NUM>. The insulated line <NUM> is coupled to the tank via a valve <NUM> and a gas return valve <NUM> for filling the tank <NUM>. The tank <NUM> further comprises two pressure release valves <NUM> so that the pressure in the tank <NUM> does not reach dangerous levels. In the example shown, the filter apparatus <NUM> also comprises two pressure release valves <NUM>. One of the pressure release valves <NUM>, <NUM> may be set to a normal operating pressure of the apparatus, and the other may be set above the normal operating pressure but below a maximum safe operating pressure, for example.

In some examples, as shown in <FIG>, the insulated line <NUM> may be coupled to a separate feed line <NUM>, for example proximal to the valve <NUM>, however in other examples it will be understood that the insulated line <NUM> may act as a feed line. In the example shown in <FIG>, also coupled to the insulated line <NUM>/feed line <NUM> inside the tank is an optional spray bar <NUM> that can act to supply liquid coolant (for example recovered liquid coolant recovered from the recuperator <NUM> described above) in the form of a spray over liquid coolant stored <NUM> stored in the tank <NUM> so as to cool the stored liquid coolant <NUM>.

The arrangement of the tank <NUM> illustrated in <FIG> is such that no trapped volumes of liquid coolant exist, and so that the pressure in the reservoir <NUM> never goes sub-atmospheric. In some examples there are two valves, for example on the line <NUM>, arranged in parallel so that if one ices there is no trapped volumes of liquid coolant and so that the pressure in the reservoir <NUM> does not increase. The tank <NUM> is also arranged to reduce the number of heat leak paths occur and take liquid coolant from near the bottom of the tank <NUM>.

<FIG> is a graph showing how work and mass change with the introduction of water and liquid nitrogen (as example liquid coolants) in the compression cylinder of a split-cycle engine apparatus, for example the split-cycle engine apparatus described above. At Point A there is no LN2 or water added. The starting point on the Y axis intersections are two families. Above A is the percentage mass compressed each stroke of the compressor as the amount of liquid nitrogen (LN2) is increased with each line representing an increase in water. In each case the amount of air entrained into the compression cylinder is constant.

Below A the graph illustrates the same increases in mass of water and LN2 but shows how the specific work changes. The point identified is where the mass compressed per stroke reaches <NUM>%, but where the specific work required to do this is only about <NUM>-<NUM>% if no liquid nitrogen or water were added. This is an important point with a <NUM>-cylinder engine as a compression cylinder could be removed completely from the engine, reducing friction and pumping losses, whilst still producing the same amount of specific work as a conventional <NUM> cylinder engine.

It is notable that at this point the O2 molecular concentration is reduced to <NUM>% that of normal air (under standard conditions). Depending on the load point, it may be desirable to either use liquid air or add liquid oxygen instead of the LN2 to facilitate a larger fuel load. Typically, there will be an excess of oxygen present, but it may be necessary to add more oxygen when the engine is experiencing a high demand.

In some embodiments, the air drawn into the compression cylinder <NUM> may be intercooled first. This increases the density of the air, however it results in lost heat as the air in the compression cylinder <NUM> is colder (which may be inefficient for combustion). The engine may be configured so that before the air enters the compression cylinder <NUM>, the incoming air is in a heat exchange relationship with one of the liquid coolants, for example water, such that the air is cooled and the water is warmed prior to injection into the compression cylinder <NUM>.

<FIG> shows the effect of changing the feed temperatures for the air being drawn into the compression cylinder and the water being injected into the compression cylinder as a liquid coolant. In <FIG>, before being drawn into the compression cylinder <NUM>, the incoming air is cooled by using it to heat the water. By providing cooler air, the air density increases which allows for a greater mass of air to be fed into the compression cylinder <NUM>. A greater mass of air comprises more oxygen, which may be desirable for combustion. <FIG> shows that a greater percentage mass of working fluid per stroke may be achieved when using cooler/denser air.

An effect of providing more air into the compression cylinder <NUM> and/or pre-warming the water is to cause the boiling temperature of the water in the compression cylinder <NUM> to increase. This may enable the water to absorb more heat before it vaporises.

With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit.

It is to be appreciated in the context of this disclosure that although reference has been made to two or three liquid coolants being used, this is not considered to be limiting, as more liquid coolants may be used. Additionally, the liquid coolants may be pre-combined before being injected together into the compression cylinder <NUM>, or they may be injected separately. The controller <NUM> may determine a mixture of coolants based on the demands and thermodynamic variables of the engine. For example, the controller <NUM> may determine that more oxygen should be added to the compression cylinder <NUM>, and accordingly, the controller may pre-mix an oxygen-containing coolant with another coolant to a selected ratio at which the oxygen demands will be met.

There may be a connection between liquid coolant reservoirs controllable by the controller <NUM> so as to enable the pre-mixing of the coolants. Alternatively, the injector may have two fluid inlets, and the controller <NUM> may control the flow of each fluid into the injector to meet the selected ratio of coolants in the mixture. Accordingly, the coolants may be pre-mixed prior to injection, with the mixture being at a selected ratio, which may be determined and controlled by the controller <NUM>.

In some examples, one or more memory elements can store data and/or program instructions used to implement the operations described herein. Embodiments of the disclosure provide tangible, non-transitory storage media comprising program instructions operable to program a processor to perform any one or more of the methods described and/or claimed herein and/or to provide data processing apparatus as described and/or claimed herein.

Claim 1:
A filter apparatus (<NUM>) for removing solid contaminants from a cryogenic liquid which has been condensed into its liquid phase via a refrigeration process, and wherein the cryogenic liquid is to be injected into a compression cylinder (<NUM>) of a split cycle internal combustion engine (<NUM>), and wherein the filter apparatus (<NUM>) comprises:
a liquid inlet (<NUM>);
a liquid outlet (<NUM>) wherein the liquid inlet (<NUM>) is coupled to the liquid outlet (<NUM>) via a filtering element (<NUM>, <NUM>), the filtering element (<NUM>, <NUM>) comprising a first portion (<NUM>) and a second portion (<NUM>);
a diverter (<NUM>, <NUM>) arranged to direct the liquid through the first portion of the filtering element (<NUM>) and, in response to a control signal, direct the liquid through the second portion (<NUM>) of the filtering element;
wherein the apparatus (<NUM>) is configured to heat a respective one of the first and second portions of the filter while liquid is diverted away from said portion and the other one of the first and second portions of the filter is operated to filter liquid coolant in the liquid coolant flow path.