Systems Operation

Usage:

System Description

A hydrocarbon fuel (ethanol) is injected into an oxygen rich exhaust environment. The hydrocarbon fuel and exhaust gas mixture passes through a catalyst bed where NO_x is significantly reduced.

The system consists of three subsystems:

1. A control box.

2. A hydrocarbon fuel injection group.

3. A converter/muffler.

The control box and hydrocarbon fuel injection group are mounted on the engine. A catalytic converter is incorporated in the converter/muffler and shipped with the engine.

DeNO_x Control Box
(1) Control box. (2) Monitoring system display module. (3) Service/Normal switch. (4) Clear/Normal/Mode switch. (5) Customer harness connector. (6) Service tool connector. (7) Engine harness connector. (8) Hydrocarbon fuel return. (9) Hydrocarbon fuel supply. (10) Pressurized hydrocarbon fuel to injectors.

DeNO_x Control Box (door open)
(2) Monitoring system display module. (11) ON/OFF switch. (12) Circuit breakers. (13) Pressure regulator. (14) Filter assembly. (15) Hydrocarbon fuel pump relay. (16) Hydrocarbon Injection Control (HIC). (17) Hydrocarbon fuel pump. (18) Hydrocarbon pressure sensor. (19) Change filter differential pressure sensor. (20) Main circuit breaker. (21) Memory volt supply circuit breaker.

The control box (1) houses the Hydrocarbon Injection Control (HIC) (16), monitoring system display module (2), hydrocarbon fuel pump (17), filter assembly (14), ON/OFF switch (11), circuit breakers (12), hydrocarbon fuel pump relay (15) and the pressure regulator (13). The HIC determines the amount of hydrocarbon fuel that needs to be added to the exhaust and modulates the hydrocarbon fuel injectors to deliver the required amount of hydrocarbon fuel. The monitoring system provides system data to the operator. The operator is alerted to any potential problems or maintenance requirements. The hydrocarbon fuel pump, filter assembly and pressure regulator supply filtered, pressurized hydrocarbon fuel to the injectors for delivery into the exhaust. The control box is mounted on the opposite side of the engine from the engine instrument panel. The hydrocarbon fuel tank, hydrocarbon fuel supply lines to the control box, hydrocarbon fuel return lines from the control box, tank mounted hydrocarbon fuel level sensors and exhaust piping to the converter/muffler are customer supplied.

(22) Hydrocarbon fuel supply line. (23) Cooled block. (24) Hydrocarbon fuel injectors.

The hydrocarbon fuel injectors (24) are mounted in a cooled block (23) flanged to a special casting mounted to the exhaust outlet on one bank of the engine's exhaust system. The block is cooled with engine coolant. The signal that controls the injectors comes from the HIC in the DeNO_x control box. System wiring will be incorporated in the engine wiring harness.

The catalytic converters are mounted in a converter/muffler system.

Hydrocarbon Injection Block Diagram

System Function

The DeNO_x catalyst system is a computer controlled device utilizing hydrocarbon fuel injection in combination with a proprietary catalyst to reduce NO_x emissions. The system is controlled by the Electronic Control Module which has been programmed to serve as the Hydrocarbon Injection Control (HIC).

The Engine Control Module communicates to the HIC the engine speed, fuel delivery rate and separate circuit aftercooler temperature. The HIC uses this information to determine the amount of hydrocarbon fuel to be injected for the desired NO_x reduction. The HIC then controls the hydrocarbon fuel injectors to deliver the desired amount of hydrocarbon fuel into the exhaust system.

The DeNO_x catalyst system will reduce NO_x from the engine exhaust by approximately 80 percent. The reduction is possible for catalyst inlet temperature between 420 to 520°C (788 to 968°F). The catalyst performance is reduced at lower inlet temperatures.

Hydrocarbon Fuel Injection

Hydrocarbon fuel is injected into the engine exhaust stream at a controlled rate based on engine speed, fuel delivery rate, and separate circuit aftercooler (SCAC) temperature. The actual values of engine speed, engine fuel delivery rate, and aftercooler temperature are measured by the Engine Control Module and passed to the Hydrocarbon Injection Control (HIC) over the CAT data link. The HIC then determines the injection rate by interpolation of measured SCAC temperature and the injection rates indicated by the Emissions Maps. The Emissions Maps have been generated from lab testing (NO_x vs. rack at a given SCAC temperature) and some specific load points can be found in TMI. The HIC then determines the pulse rate required to deliver the correct hydrocarbon fuel rate from the Injection Delivery Map. The HIC then activates the injector to deliver hydrocarbon fuel at the desired rate.

Injection Delay

Hydrocarbon fuel injection will be delayed when the system is too cool for the catalyst to convert oxides of nitrogen. This reduces unnecessary hydrocarbon fuel usage.

When the engine is first started, hydrocarbon fuel injection is delayed until the engine speed exceeds 600 rpm and the calculated catalyst temperature is at least 300°C (572°F).

Engine Speed

Engine Speed provides intelligence to the Hydrocarbon Injection Control (HIC) to delay start of injection until the catalyst is warmed up. This reduces unnecessary hydrocarbon fuel usage.

The engine speed is passed to the HIC from the Engine Control Module via the CAT data link. If the engine speed drops below 600 rpm, hydrocarbon fuel injection is inhibited until the engine speed exceeds 600 rpm and the calculated catalyst temperature is at least 300°C (572°F).

Hydrocarbon Fuel Pump Activation

24 VDC is applied to a relay which activates a positive displacement pump which delivers the hydrocarbon fuel to the injector(s). This provides an automated method of powering the system only when required.

When the engine has been running at a power level that would normally require hydrocarbon fuel injection for at least 20 seconds, the engine speed exceeds 600 rpm, the calculated catalyst temperature is at least 300°C (572°F), the Hydrocarbon Injection Control (HIC) provides 24 VDC signal to the relay which drives the pump transferring the hydrocarbon fuel from the storage tank to the injector(s) located in the exhaust stream.

Whenever the engine has been stopped (engine speed below 600 rpm detected) the pump will be shut off. The pump will not be turned on again until the engine speed exceeds 600 rpm and the calculated catalyst temperature is at least 300°C (572°F).

Whenever the engine has been operating at a power level that does not require hydrocarbon fuel injection for over five minutes, the HIC will shut off the pump.

After the pump has been shut off, the pump will restart when the engine returns to a power level that would normally require hydrocarbon fuel injection and remains there for 20 seconds if the engine speed exceeds 600 rpm and the calculated catalyst temperature is at least 300°C (572°F).

Hydrocarbon Fuel Injection Control On/Off Record

Hydrocarbon fuel injection control On/Off Record provides a record of when the DeNO_x System was turned off while the engine was running. Hydrocarbon fuel injection control on/off record will also provide verification of when the DeNO_x system was enabled as a function of the engine hour meter reading.

Whenever the engine is running, the Hydrocarbon Injection Control (HIC) requests and records the engine hour meter reading at least once per hour. When power is first applied to the HIC, the HIC requests the current engine hour meter reading. The HIC compares it to the last recorded engine hour meter reading. If the difference is greater than two hours, the system records the previous reading as the time when the HIC was shut off while the engine was running. The HIC records the current reading as the time when the HIC was turned back on.

The resulting readings are stored in a file and can be retrieved by the service tool to establish when the HIC was turned off as a function of engine operating hours. The record covers the last six on/off cycles. The on/off time is recorded to the nearest two hours.

System Monitoring

The DeNO_x catalyst system is equipped with a monitoring system. The HIC monitors the operation of the total system and communicates to the operator through the monitoring system display module. The monitoring system display module can scroll through hydrocarbon fuel usage, total hours on the hydrocarbon fuel pump and hydrocarbon fuel system pressure by pressing the service switch. The display present when the switch is released will continue to be displayed until the service switch is activated again. Hydrocarbon fuel usage will be displayed when the system is powered up.

There are eight alert indicators that are used by the system. They are:

System FailureCheck SystemHydrocarbon Fuel EmptyHydrocarbon Fuel LowSystem LeakChange FilterCatalyst TemperaturePressure Fault

Alert Indicators

System Failure

The system failure fault will immediately shut down the DeNO_x system. The "System Failure" indicator will flash when the "Hydrocarbon Fuel Empty" indicator is activated or when other conditions occur that could cause serious consequences if the system continued to try to operate normally.

Hydrocarbon Fuel Empty

Hydrocarbon fuel empty indicator alerts the operator that the hydrocarbon fuel tank is empty. A customer supplied on/off level switch in the tank opens when the hydrocarbon fuel tank is empty. If the switch is open for ten seconds the Hydrocarbon Injection Control (HIC) will turn on the "Hydrocarbon Fuel Empty" indicator, turn off the hydrocarbon fuel pump, turn on the "System Failure" indicator, and enter an event that hydrocarbon fuel was not available. The DeNO_x system will be disabled until the operator clears the event by doing a system reset or adds hydrocarbon fuel (ethanol). If the customer does not provide an empty hydrocarbon switch, pin-4 and pin-8 on the customer harness plug need to be connected together ("jumpered").

Hydrocarbon Fuel Low

The hydrocarbon fuel low indicator alerts the operator that the hydrocarbon fuel tank is low. A customer supplied on/off level switch in the tank opens when the hydrocarbon fuel level is less than ten percent (or whatever is defined as low). When this switch is open the Hydrocarbon Injection Control (HIC) turns on the "Hydrocarbon Fuel Low" indicator. If the customer does not provide an empty hydrocarbon switch, pin-4 and pin-10 on the customer harness plug need to be connected together ("jumpered").

System Leak

The system leak indicator alerts the operator of a leak in the DeNO_x system. This check is performed automatically when the engine is started, and then once every eight hours when the engine is running continuously. Pressure is measured just before shutting the hydrocarbon fuel pump off. The pressure is measured again after the hydrocarbon fuel pump has been off for thirty seconds, with the injectors off. If the pressure difference between the two readings is greater than 100 kPa (15 psi) the "Check System", "System Failure" and "System Leak" indicators will be turned on and the system will shut down. The indicators can be shut off by a system reset.

Change Filter

The change filter indicator alerts the operator of a filter restriction. It will provide the operator with an indication of when the filter needs changed based on filter condition instead of operating hours. A pressure differential switch in the filter housing closes when the pressure drop across the filter reaches a predetermined level. When the switch closes, the "Change Filter" indicator is turned on and a "Filter Change Due" event will be recorded. If the switch remains closed for 100 hours, the "System Failure" indicator will be activated.

An "Overdue Filter Change" event will be recorded and the DeNO_x system will be shut down. The system will be disabled until the operator changes the filter and does a system reset.

Catalyst Temperature

The catalyst temperature indicator alerts the operator of high exhaust temperature. The engine exhaust manifold temperature is monitored. If the temperature exceeds 725°C (1337°F) the Hydrocarbon Injection Control logs a "High Catalyst Temperature" event and turns on the "Check System" and "Catalyst Temp" indicators. If the temperature goes above 750°C (1382°F), the Hydrocarbon Injection Control logs a "High Catalyst Temperature" event and shuts down the DeNO_x system. The "System Failure", "Check System" and "Catalyst Temp" alert indicators are turned on.

Pressure Fault

Low Hydrocarbon Fuel Pressure

A sensor provides a 0 to 5 volt signal proportional to the absolute pressure out of the hydrocarbon fuel pump to the Hydrocarbon Injection Control (HIC). If the pressure drops below 440 kPa (64 psi) during normal operation for three seconds after pressure has been established, when the HIC has turned the hydrocarbon fuel pump on, the HIC shuts off voltage to the hydrocarbon fuel pump, stops activating the injectors, logs a "Low Pressure" event and turns on the "System Failure", "Check System" and "Press Fault" indicators. This alerts the operator that the hydrocarbon fuel injection system is not functional. The alert indicators are also turned on and an event is logged if pressure is not detected within twenty seconds after the HIC provides voltage to the hydrocarbon fuel pump.

High Hydrocarbon Fuel Pressure

A sensor provides a 0 to 5 volt signal proportional to the absolute pressure out of the hydrocarbon fuel pump to the Hydrocarbon Injection Control (HIC). If the pressure goes above 570 kPa (84 psi) during normal operation for three seconds after pressure has been established, when the HIC has turned the pump on, the HIC logs a "High Pressure" event and turns on the "Check System" and "Press Fault" indicators. If the pressure goes above 688 kPa (99 psi) during normal operation for three seconds after pressure has been established, when the HIC has turned on the hydrocarbon fuel pump, the HIC logs a high pressure event, shuts down the DeNO_x system, and turns on the "System Failure", "Check System" and "Press Fault" indicators.

Check System

The check system indicator alerts the operator that something is wrong with the system. This indicator will be on in addition to another indicator except in the case of a failed plugged injector test. If a plugged injector test is failed, the "Check System" light will be on with no other indicators on. The indicator will stay on until the operator clears whatever is wrong.

Pump Relay Electrical Failure

The pump relay electrical failure detects an electrical failure or pending electrical failure of the hydrocarbon fuel pump relay. This will reduce maintenance costs and reduce downtime.

The standard diagnostic circuits check for abnormally high or low resistance to detect an open or shorted hydrocarbon fuel pump relay. If either of these conditions is detected, a diagnostic is logged and the "Check System" indicator flashes. The system will continue to operate unless a higher level diagnostic or event (low hydrocarbon fuel pressure) is detected. The "Check System" indicator can be shut off by eliminating the electrical failure. The logged diagnostic can be cleared by using the Diagnostic Code clear function (Mode 1) after the problem is corrected. The diagnostic will automatically be cleared after 100 hours of operation after the problem is corrected.

Injector Plugging

The injector plugging will provide an indication of abnormal hydrocarbon fuel injector(s) restriction. This will provide an indication the DeNO_x system is not delivering the correct amount of hydrocarbon fuel.

This check is performed when the engine is started, and once every eight hours while the engine is continuously running. The pressure is measured 30 seconds after shutting the hydrocarbon fuel pump off, with the injectors closed. The injectors are opened immediately after the pressure is measured, and a second measurement is taken three seconds after the injectors are opened. If the pressure difference between the two readings is not greater than 70 kPa (10 psi), the injectors are plugged. The "Check System" and "System Failure" indicators will flash, an event will be logged, and the Hydrocarbon Injection Control will shut down the DeNO_x system. The "Check System" and "System Failure" indicators can be shut off by a system reset or by using an electronic service tool.

Diagnostics And Events

Diagnostics are distinguished from Events both by their nature and by their storage location. A diagnostic indicates the Hydrocarbon Injection Control has detected an invalid signal for an input, an improper feedback for an output, or an internal error (sensor input grounded, sensor input shorted to + battery, personality module mismatch, etc.). An event indicates that the DeNO_x system is experiencing improper operation, usually due to a mechanical failure or external condition. Events Do Not indicate there is a problem or failure with the Hydrocarbon Injection Control. An event can indicate a non-electronic problem with the DeNO_x system (low hydrocarbon fuel, low hydrocarbon fuel pressure, system leak, etc.). Events will not be logged if there is a diagnostic with that part of the system. This separation is further distinguished by using separate display areas on the electronic service tool. The diagnostics can also be displayed on the Caterpillar Monitoring System display.

Diagnostic Code Display

Two methods of displaying information about diagnostics are provided. Onboard Hydrocarbon Injection Control display is done by the Caterpillar Monitoring System. This system displays the CID-FMI codes. The off board display is done via the electronic service tool which uses the CID-FMI in combination with descriptive text to avoid mistakes in interpreting the codes.

CID-FMI: This method of diagnostic code display uses a two part code. The Component Identifier (CID) identifies the specific component for which the diagnostic was detected. The Failure Mode Identifier (FMI) identifies the mode of the failure detected. Together, the two parts of the code allow consistent identification of the problem.

Diagnostic Code Chart

Event Code Display

An event is logged in the Hydrocarbon Injection Control (HIC) memory. Events will not be displayed on the Caterpillar Monitoring System display. Use of an electronic service tool is necessary to display events.