Hendon Publishing - Article Archive Details

Advanced Technology Presents Maintenance Challenges

“Change is in the air.” Nowhere is this more apparent than in the automotive technology found in our new generation of police, special service and admin vehicles. Ford, General Motors and Chrysler have all incorporated fuel saving and power-enhancing features into almost every make and model they support. From improved gasoline engines to a wider selection of diesel platforms, all serve to deliver better power, performance and economy.

So what are the motivators for this change? One is the ever-tightening noose of vehicle emissions. With the emphasis on environmental stewardship gaining ground, all manufacturers are doing their part to reduce their “carbon footprint.”

Coupled with this “green” wave, is the government push for improvement in fuel economy (CAFE). As of mid-2011, an agreement was reached between the U.S. government and 13 large automakers to increase fuel economy to 54.5 miles per gallon for cars and light-duty trucks by model year 2025.

To begin with, the automotive industry is able to deliver on all these changes by reviewing current technology. From internal and rolling friction to a variety of fuel, all areas of potential efficiency gains were evaluated. In the end, some striking discoveries were made.

First, fuel injection and combustion dynamics have made vast advances recently, thanks largely to the work of European automotive engineers. Key areas like fuel injection, piston design, air control, frictional loss, and air-to-fuel ratios have all undergone remarkable evolutions. It is no secret that engine designs have remained somewhat stagnant in recent years. So how best to reinvent what we have, while keeping the best of what we need? That is where automotive innovation comes into play.

While adopting more powerful and leaner operating engine configurations, OEMs have successfully created a balance between environmental compliance, while delivering on operational demands. Older engine technologies are being systematically sidelined in order to bring forth newer engine configurations that surpass anything we’ve seen so far.

Taking center stage and the backbone of these technology changes is Gasoline Direct Injection (GDI) and Turbo Diesel Injection (TDI) engine. To review, previous fuel injection models relied on indirect injection of the fuel spray outside the combustion chamber at a stoichiometric ratio of 14.7:1 air-to-fuel. Typical piston compression ratios were limited to about 9:1 in gasoline and 20:1 in diesels due to the limits of squeezing this finite volume of incoming air.

However, Direct Injection has completely reinvented this piece of physics by allowing for more air to enter the engine while reducing the amount of fuel required for ignition. Ultra-lean fuel mixtures as high as 65:1 have been achieved in some models while the average ratios hover around roughly 25:1 on average. This is a quantum leap from the 14.7:1  limit from which we came.

One good example of this new direct injection (gasoline) engine is found within the Ford EcoBoost. The EcoBoost model is well on its way to becoming the most popular engine in its class. The 3.5L EcoBoost achieves an impressive 355-365 hp @5700 rpm, and 350 lb·ft torque, and delivers power like no other. It contains some truly impressive engineering innovations.

From twin variable turbochargers spinning at 170,000 rpms to fuel injection pulses varying from low-pressure ultra-lean micro droplets to richer 3,000 psi squirts, this engine can make gobs of power at the mere touch of the pedal. Even the pistons have a specific concave indentation, to facilitate high turbulence within the combustion chamber for optimum fuel-air mixing.

All this comes with a credible fuel economy rating of 19 City and 29 Highway mpg. This equates into about 20 percent improved mpg and 15 percent reduced emissions as compared to normal air aspirated (14.7:1 air-to-fuel) engines of similar displacement.

The real magic to this Direct Injection engines lies within the controlled and exacting dispersal of smaller and fewer fuel droplets to optimize (and not waste) fuel. Smaller fuel droplets create more surface area for super-critical spark ignition. Even the piston rings have changed. Older engines relied on piston rings “pushing out” or “sealing” the cylinder at roughly 20 psi force. 

New direct injection engines use “lower tension” piston rings. These new LT rings reduce frictional drag within the cylinder by only expanding with as little as 7-8 psi force. This reduces the frictional drag between lubricating engine oil and cylinder wall. Direct injection engines in general, and EcoBoost engines in particular, represent the optimization of engine power and performance.

That is the good news. Here is the not so good. For with every improvement, there usually comes with some degree of compromise. Significant problems can quickly develop within the EcoBoost’s high-pressure (2150 psi) fuel injection system and combustion chamber. Fuel quality, oil evaporation and hydrocarbon deposits are the bane of these engines. In order to maintain and reap the benefits of this highly advanced engine, there is no room for disruptive fuel injector fouling or oily piston deposits.

In older port-fuel injection, the fuel spray had a cleaning effect on the intake valves and pistons, since it washed them with every injection fuel pulse. Clean valves are good, dirty valves are bad, it’s that simple. When EcoBoost intake valves accumulate oil and fuel deposits, this disrupts the ability of the engine to gobble air and disperse fuel properly. Our study shows progressive loss of power and economy raises emissions. 

Under the ultra-lean injection in EcoBoost, it is paramount to maintain the quality and quantity of fuel spray and air-swirl dynamics. If you don’t, then you are likely to set a misfire code or experience engine stumble. Impede and rob the cylinder of enough air, disrupt the precise turbulence required for fuel ignition, and you might as well speed dial your tow service. Under continued operation in this condition, it wouldn’t be long before you start to risk creating irreversible engine damage through cylinder overheating.

As countless online videos can show, direct fuel injection engines do not have a mechanism to clean the intake valves. The intake valves only shuttle incoming air, and air does very little cleaning. Adding salt to the wound is the fact that evaporating engine oil usually migrates back into the incoming air stream through the PCV, which further increases the amount of nasty goop that dries rock hard onto the valves. So much material eventually coats the valve stems and tulip area that combustion chamber sealing can be compromised.

Studies have shown that normal pump fuel has little ability to keep the intake valves and pistons clean. However, the periodic use of high-quality fuel detergents was shown to greatly reduce the build-up of these interfering deposits.

Don’t lose hope. While EcoBoost and similar DI engine designs do have some valuable gains albeit unique sensitivities, they can be well-maintained by understanding a few important points. Number one is that quality in delivers quality out. From engine oils, to fuels, all play a key role in keeping these engines operating at peak performance. 

(Ed. Note: Future articles will address the value and protection offered by full synthetic engine oils, engine oil analysis, and fuel treatment in maintaining these highly engineered direct injection engines.)

Michael Belluomo is the Technical Service Manager for BG Products, Inc. He can be reached at mbelluomo@bgprod.com.

Published in Police Fleet Manager, May/Jun 2014

Rating : 5.4

Comments 0 Comments

No Comments

Article Images

Click to enlarge images.

Events and Tradeshows: LAOPFMTRPSIT
Close ...