By David Rowland
Tier 2? Tier 3? Interim Tier 4? Tier 4? To many of us, the aforementioned are meaningless terms. Thanks to EPA, these terms will haunt main engine, generator set and auxiliary power unit purchasers in future years, along with acronyms such as EGR, SCR, DOC, DPF, and a multitude not mentioned.
In the past, there’s been a lot of confusion, and sometimes misinformation about how diesel engines are affected by the EPA tier system. Going to the EPA website only furthers, in my opinion, the confusion. After trying to decipher the language the website used, which I strongly suspect deviates from US English, I determined their postings were only decipherable with the assistance of a couple of attorneys and a cadre of engineers. Continued pondering of these websites might, in my opinion, cause serious brain damage to the beholder, from a modern day Hydra.
I recently came into possession of one of the most concise and easily understandable presentations regarding the ramifications and timelines of the EPA tier system. FPT Powertrain Technologies prepared a 62-page outline of the benefits and disadvantages of the various systems that will come available on future engines. FPT, for those who are unaware, is Fiat, the largest equipment manufacturer in Europe, and owner of recognizable equipment companies such as Case, New Holland, and Kobelco and FPT marine and industrial diesel engines.
The main pollutants produced by diesel combustion are CO (carbon monoxide), HC (hydrocarbons), NOx (nitrogen oxide) and PM (particulate matter). Carbon monoxide is odorless, tasteless, and colorless, but highly toxic. Hydrocarbons are unburned organic elements found in both fuel and engine oil that are not completely burned in the combustion process. Nitrous oxides are generated during high temperature combustion. PM is composed mainly of small carbon particles generated by incomplete combustion of diesel fuel.
In 2011, interim Tier 4 regulations go into effect for all engines of more than 175 horsepower, then will be extended to other power ranges. Compliance will significantly reduce NOx by 50 percent and PM by 90 percent. In order to meet compliance, engines in this power range will be electronically governed using high-pressure common rail or unit pump injectors.
Additionally, some of the following equipment will be required to meet emission standards: (a) External exhaust gas recirculation (EGR), (b) Diesel oxidation catalyst (DOC), (c) Diesel particulate filter, (d) PM – CAT, and (e) Selective catalytic reduction (SCR). EGR and SCR systems are now widely used on highway trucks and construction equipment.
The EGR systems I’ve seen are similar to a muffler. A portion of the exhaust gas passes through a muffler-like device, and is diverted back into the air intake system. The EGR is usually cut off when the load factor does not require EGR. EGR reduces NOx by lowering the combustion temperature. But, because the temperature is lowered, PM is generated. DPF or PM-CAT are used to control the PM.
SCR systems include the injection of a urea/water mix into the exhaust. The chemical reaction caused by the injection converts NOx into nitrogen (N2) and water (H2O). The water/urea mixture is non-toxic, but may faintly smell of ammonia and must be highly pure in composition. The government designation for the mix is “Diesel Exhaust Fluid.” A dosing control unit inside a supply module regulates the injection. This system requires a supply module, a water/urea tank, a dosing module, and an SCR catalytic converter. Should the supply of urea go dry, the engine will go into a reduced power mode. Urea tanks will need to be refilled when fueling. Truck stops and fleet fueling stations are now installing urea dispensing equipment. (Note I was quickly told that replumbing the liquid flow from the marine head to the urea tank doesn’t work.)
The benefits of the EGR technology include no need for a second fluid or fluid tank space, and the small size and simplicity of the system. The disadvantages include reduced power density, shorter maintenance intervals, increased engine cost, and requirement of larger radiators or cooling systems. Additionally, the DPF requires replacement after 4,000 hours of operation.
The benefits of the SCR technology provide better fuel consumption, longer maintenance intervals, no additional heat rejection, and a system good for life. The disadvantages include the need for a second engine fluid, tank installation, and a more complex exhaust system. According to a preliminary analysis, SCR equipped engines will enjoy an overall savings of 3 percent to 4.5 percent compared to current costs for equal power.
Electronic engines are going to be quirky. Instead of a mechanical throttle cable arrangement, a potentiometer will be used to control engine speed. Engines will be fitted with an ECU (computer brain box) and a multitude of sensors. The sensors will regulate the timing of the engine and the flow of fuel based on operating conditions. If a sensor gets a fault reading, the engine may go into a reduced power mode, or may simply shut down until the fault condition is remedied. Most of the electronic engine control panels I’ve seen to date usually provide a readout of the fault condition, or at least provide a warning light for the fault. If the condition is minor, and the engine operator is lucky, the fault condition might be remedied and normal operation can resume. I’ve heard several stories of boats being towed in when luck didn’t prevail.
Crowded engine compartments or engine rooms are going to become more crowded. Exhaust piping will certainly become more complex. Electronic plugs, cables and sensors are delicate – not to be stepped upon when climbing around an engine compartment.
Moisture is a major enemy of the new electronic engines. Care should be taken to minimize exposures. I’ve seen more than a few engine compartments with engines and pipes cloaked in rust. Electrical connections, according to some reports I’ve heard, are a source of problems. A little moisture can cause corrosion in the plug, thus providing faulty readings to an engine’s computerized control system. Coating plug ends with dielectric grease, which provides protection from moisture, can mitigate this situation.
There’s still time to repower with mechanical technology. Several marine engine manufacturers have old technology engines still available under current EPA regulations. If considering a repower, it might be timely to do so before the acronyms become everyday life.