Cummins QSX15

The Cummins ISX is an Inline (Straight)-6 diesel engine produced by Cummins for heavy duty trucks and motorcoaches, replacing the N14 in 2001 when emissions regulations passed by the EPA made the engine obsolete. Originally called the "Signature" series engine, the ISX uses the "Interact System" (hence the "IS" which is the moniker for the full authority, on highway fuel system Cummins pioneered) to further improve the engine. This engine is widely used in on highway and vocational trucks and is available in power ranging from 430 hp all the way to 620 hp 2050 lb-ft. The QSX is the off-highway version of the ISX with the Q standing for Quantum. The QSX is used for industrial, marine, oil & gas and other off-highway applications. Cummins also produced a 650 hp and 1950 lb-ft version for the RV market. It has proven to be unreliable and Cummins has issued several "fixes" for it but no warranty coverage extension.

Until 2010 this engine was a dual overhead cam design with one cam actuating the injectors and the other the valve train. This injection system is known as HPI (high pressure injection) where the injectors are cam-actuated to create injection pressure. The fuel system uses an Integrated Fuel System Module (IFSM) with a lift pump, gear pump, pressure regulators, shutoff valve, metering and timing actuators to deliver fuel to the injectors. It has a one piece valve cover that is either plastic or on older models a chrome plated steel cover otherwise known as the Signature 600 or ISX CM570.

In 2002, the ISX CM870 brought cooled Exhaust Gas Recirculation (EGR) which takes exhaust gas and recirculates it back into the intake of the engine lowering the combustion chamber temperatures limiting the formation of NOx.

In 2008, Cummins unveiled the ISX CM871, this engine featured a Diesel Particulate Filter (DPF) which trapped the particulate matter or "soot" produced in the engine. With the help of the Diesel Oxidation Catalyst (DOC) the soot trapped in the DPF is oxidized and turned to ash during a process called regeneration.

The current EPA 2010 version known as ISX15 CM2250 features enhanced Exhaust Gas Recirculation, Diesel Particulate Filter and Selective Catalytic Reduction (SCR), also known as Urea Injection. SCR consists of a Diesel Exhaust Fluid (DEF - composed of urea and water) injection system: holding tank, pump, controller, and injector and an SCR catalyst brick. DEF is heated, pumped and injected into a decomposition tube which then reacts with the exhaust reducing NOX. The ISX15 CM2250 and CM2350 has eliminated the injector camshaft due to the advent of the common rail fuel system in which the fuel is pressurized from a high pressure, multiple piston pump, transferred through tubing to a rail where fuel is stored under extremely high pressures up to 35,000 psi.

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