At the beginning of the year construction equipment manufacturers were required to have a majority of their new off-highway diesel engines meet the EPA’s stringent Tier 4 Final emission standards. Because of this you can expect to start seeing a lot more of these new high-tech machines at jobsites, rental companies and your local dealers in the coming months. Tier 4 Final is the latest step in the EPA’s nearly 20-year process to get emissions to near-zero levels. This included reducing emissions of nitrogen oxides (NOx) to 0.3 g/bhp-hr and particulate matter (PM) to 0.015 g/bhp-hr both of which reflect a 96 percent reduction from Tier 1 levels.
To accomplish this massive reduction in emissions, construction equipment manufacturers have spent years researching and developing technology to get emission levels reduced to the required levels while still providing the same power and performance that customers have come to expect from previous models. Today we’ll take a look at some of the technologies manufacturers have incorporated emissions reduction components into their diesel engines as well as the aftertreatment systems that have been added in order to reach Tier 4 emission levels. We’ll also take a look at how a few of the construction equipment manufacturers are utilizing all or a combination of these technologies based on engine size and application.
Emissions Reduction Components
High Pressure Fuel Systems – The most popular system being used by manufacturers is a high pressure, common rail fuel injector that feeds individual solenoid or piezoelectric valves. This system allows for more injection per stroke and better control over the fuel injection amount which results in better atomization of the fuel and lower emissions.
Turbochargers – Forces extra air into the combustion chamber that results in increased power and energy efficiency. Most manufacturers are either using a twin turbocharger system that consists of a large and small turbocharger or a variable geometry turbo charger to achieve the optimal aspect ratio when operating at either low or high engine speeds.
Exhaust Gas Recirculation (EGR) – This process involves redirecting some of the exhaust gas back into the engine. The exhaust gas is typically cooled with a heat exchanger before being reintroduced into the engine where it reduces the production of NOx by lowering the combustion chamber temperature.
Diesel Oxidation Catalyst (DOC) – A honeycomb shaped device that is coated with a catalyst such as palladium or platinum and aluminum oxide. When the exhaust passes through the DOC a chemical reaction occurs that converts the carbon monoxide into carbon dioxide and the hydrocarbons into water.
Diesel Particulate Filter (DPF) – This device removes a large amount of particulate matter (PM) from the exhaust gas. The PM gets trapped in the filter and then is burned off and oxidized. This process is called regeneration and can be done passively by either introducing a catalyst to raise the exhaust temperature or by using the exhaust heat during normal operation. Regeneration can also be done actively by introducing high heat to the filter from another heat source. The DPF has to be periodically cleaned to remove the ash that remains after the PM is burned off.
Selective Catalytic Reduction (SCR) – This system injects diesel exhaust fluid (DEF) into the exhaust stream where they mix together in a catalytic chamber that causes NOx to be converted to nitrogen and water.
Now we’ll take a look at how a few of the largest construction equipment manufacturers are incorporating these technologies into their diesel engines.
Caterpillar will be using a combination of engine emissions reduction components with aftertreatment systems on their Tier 4 Final engines. For example, their C7.1 ACERT 120-302 bhp engines will use a high pressure common rail fuels system with a single or series turbochargers. This engine will implement EGR with the Cat NOx Reduction System. The aftertreatment system will include a DOC, DPF and SCR and will perform passive regeneration. On a larger engine like the C18 ACERT 503 – 630 bhp engines will use the MEUI-C fuel system which is a mechanical electronic unit injector that controls fuel injection pressure based on the engine’s operating speed. The engine also features the Cat NOx Reduction System and a high-efficiency turbocharger. The aftertreatment system will include a DOC, DPF, SCR and a self-activating regeneration system.
Volvo Construction Equipment
Like Caterpillar, Volvo CE is using a combination of systems to control emissions based on the size and application of the engine. Their D8 215-335 hp engines will feature a cooled, external EGR system along with a high-pressure variable fuel injection system to control combustion temperatures. The aftertreatment system will include a DOC, DPF and SCR system to reduce NOx and PM. Volvo’s D11 315-355 hp engines will also feature a cooled, external EGR system along with a high-pressure variable fuel injection system, but the aftertreatment system on these engines will only consist of a SCR system.
Liebherr’s engines will feature a common rail injection system with turbochargers matched to each specific engine. The aftertreatment systems on Liebherr Tier 4 Final engines will consist solely of an SCR system, no DOC or DPF systems will be used.
If your company owns their own equipment now would be a good time to start doing some long range planning to determine when you will replace your current equipment with equipment featuring Tier 4 engines. One reason is that manufacturers will probably still continue to make replacement parts for your lower tiered equipment, they will no longer be able to manufacture engines that aren’t Tier 4 compliant. Another reason is that construction contracts on public jobs have already started mandating that all nonroad construction equipment on the jobsite be compliant with the current Tier standards.