Diesel’s new demands--the complete interview

The complete version of our interview with Michael Schena, president of Michigan Custom Machines; a shorter version of this interview appeared in the December 2005/January 2006 issue of our Automotive & Aerospace Test Report.

-- Test & Measurement World, 12/1/2005

Click here to read the print version.

Q: Please provide some background on the 2007 stricter emission standards

A: The potential for the diesel engine in the US is very big. Back in 1978, early passenger car diesels were known for their poor performance and belching smoke all to the tune of a clattery noise under the hood. The US population pretty much abandoned the notion of a diesel passenger car for the next 20 or so years.

Since then, a lot of work has been done in Europe and in the US off-highway industry to further the evolution of diesel-engine technology. Diesels are coming back. In order for diesel to be feasible, however, the level of emissions has to comply with emissions standards.

The last regulation change took place in 2002, which many of the manufacturers easily made. The next change occurs in 2007 and holds much more stringent requirements, while the 2010 standard will actually merge the emission standards for gasoline and diesel engines alike.

The biggest key to meeting these goals is in the fuel system. By going to higher pressures at the fuel-injector nozzle, the fuel can be atomized into finer droplets in the cylinder, giving more surface area and a cleaner burn. Of course, with these pressures come other challenges such as longevity of nozzles and the need for a robust high-pressure fuel source. To complicate things even more, a single injection is now split into several smaller shots that are only milliseconds apart from each other to "meter" the fuel into the cylinder at a controlled rate. The result is a quiet engine, low emissions, and…performance!

Q: What is common rail injection?

A: Common rail injection is one of three modern types of diesel fuel systems. Common rail consists of a high-pressure fuel pump capable of 2000 bar (about 30,000 psi) that feeds a heavy cast-iron vessel called the "common rail." Some engines have one or two rails depending on configuration. Special heavy-duty fuel lines feed the injectors that are actuated by an individual solenoid or set of solenoids in the injector.

Pressure in the rail can be controlled by the pump itself or by a relief valve on the rail itself. The beauty of this system is that it is very responsive and can electronically deliver fuel as often as engine revolution requires.

The other two diesel systems are the electronic unit injector (EUI) and the hydraulic EUI (HEUI). The EUI system does not have a high-pressure pump or a common rail, but instead uses an extra lobe on the camshaft and a rocker arm to actuate the injector like a valve in an engine head. The motion of the rocker arm builds pressure within the injector, which is fired electronically in sync with this event. High pressures are still achieved here, however the shot must occur during the compression of the injector tappet, and the injector has a limited volume displacement before it needs to be refilled.

The last system is the HEUI system, which is similar to a common rail system in that there is a rail and pump but instead uses engine oil, and the pressures are an order of magnitude less, near 200 bar. This oil pressure feeds an intensifier within the fuel injectors, which have a high intensification ratio. For those not familiar with the concept of an intensifier, it is a hydraulic mechanism that creates an amplified fluid pressure on one side of a piston from a lower hydraulic pressure on the opposite side, while keeping the two fluids separate.

The intensifier in our injector uses oil to drive fuel to a much higher pressure, which in turn pumps fuel through the nozzle and into the engine cylinder. Similar to common rail, the HEUI injector can be fired anywhere within the revolution of the engine, however the volume of the shot is limited to the volume of the intensifier.

Q: How does Michigan Custom Machines get involved in testing diesel engines?

A: MCM manufactures production and lab test equipment that test the components on the diesel engine such as fuel injectors, pumps, pressure transducers, EGR valves, and turbochargers. All of these components must meet a tight acceptance criterion and are 100% tested in order to guarantee an engine that will meet emissions after final assembly.

MCM has also developed the equivalent of a special engine controller we call a PFIM (programmable fuel injector module), designed for test machines that can fire diesel fuel injectors with a variety of sophisticated waveforms to simulate the split injection scenarios in the actual engine application. We are also the only certified integrator in the US for a special line of split injection flow meters called Akribis II, developed in the UK by Inov8 Technologies. Our equipment is used by major OEMs in the diesel industry, such as Caterpillar, Bosch, Denso, Detroit Diesel, Siemens, Stanadyne, and International.

Q: What are some special requirements mandated by your customers?

A: Split-injection measurement is a big one. This is a feature of fuel injection that not only requires precise actuation, but precise measurement as well. It is possible for a fuel injector to not properly dispense the correct amount of fuel for one of the splits, which would lead to poor engine performance in final testing if not caught early on. On a smaller scale, the remanufacturing and after-market industries rely on similar testing to meet OEM requirements and satisfy that "out of warranty" customer.

Q: What primary challenges lie ahead for makers of engine test and measurement equipment and instrumentation?

A: The requirements for handling higher pressure with thin, low lubricity fluids is always a challenge. These pressures will continue to increase to further improve fuel atomization, The sophistication of the fuel-injector actuation is always a challenge. Some injectors are actually using two solenoids to turn on and turn off the injection event, and in some cases, these solenoids are actually replaced by stacks of piezo crystal wafers that respond much faster than conventional magnetic devices. Of course, driving these types of actuators is totally different from conventional means. We constantly work to stay in pace with these challenges, so we can provide the best turnkey solutions for our customers.