It’s no secret that the U.S. fleet is totally at odds with it’s European counterpart in the mixture of diesel to gasoline powered cars and light trucks. And one has to wonder why diesel passenger cars are not as popular here as they are across the pond. After all, diesels are proven more efficient and more durable than their gasoline gobbling cousins, and significantly so. If in doubt, just ask Audi, the World Endurance champions for the past 15 years, running a diesel-powered car.
The 2014 Cruze diesel is taking aim at the VW Jetta TDI, and might be a real challenger.
According to a recent poll sponsored by Audi, 59 percent of American drivers between the ages of 18 and 34 polled said they would buy a light diesel passenger car if the cost of diesel fuel were on par with gasoline. At the end of 2013, diesel fuel (even though it is cheaper to produce) cost almost 60 cents a gallon more. In addition to the disparity in fuel cost, diesel-equipped models carry a higher sticker price than the same model using a more traditional engine. It doesn’t take an MIT graduate to figure out that recouping the increased costs involved would take a long time, even with the more efficient powerplant.
In Europe, those factors are almost reversed. Cost of the initial purchase might be relatively equal, but the fuel costs are not. There, diesel fuel (dependent on country) can be significantly less than gasoline. Why? Taxation. Many European countries subsidize diesel fuel with lower tax rates, resulting in a lower pump price while the U.S. tax diesel more. Add in the increased fuel economy typically enjoyed by a diesel owner, and you can understand why diesels are the more popular choice.
The 2.0-liter powerplant is based on a proven platform, with more than half a million of them sold overseas. A few U.S. models, however, were in order to meet market needs.
German manufacturers want the American trend to change and have serious advertising campaigns in place to educate American consumers about the benefits of modern diesel ownership. In addition to the basic economics, these spots are showing how today’s diesels are also quieter and cleaner than the diesels of days past.
“The market for diesel cars in the U.S. is small at present,” says Mike Omotoso, powertrain analyst at LMC Automotive. “But it is expected to grow due to Corporate Average Fuel Economy (CAFE) requirements and expected increases in gas prices. So far, the German automakers haven’t had any real competition in North America.” Until now, as at least two of the Big Three announce plans to add diesels to their model lines.
One unique American add-on was the variable swirl intake system.
GM Joins The Market
Many of our readers may recall GM’s dismal diesel forays back in the mid-1980s. The diesel Chevette and infamous Olds V-8s were well known for their failure rates. But the 2014 model year brings with it a new diesel offering, the Chevrolet Cruze. Not to be confused with its Suzuki cousin, the new Cruze started life as a globally developed platform back in 2008. It replaced the Chevy Cobalt in the North American market with its debut in the 2010 model year.
The North American version of the Cruze is built in GM’s Lordstown, Ohio, facility. Its 2.0-liter turbocharged diesel powerplant may be a new offering here, but it is hardly a new design. The basic architecture has been sold in Europe over the last 16 years under the Opel and Chevrolet nameplate and is assembled in Kaiserslautern, Germany. U.S. engineers worked with their European counterparts at GM’s Torino, Italy, design center to refine the design and insure it would meet or exceed all U.S. emissions standards.
Like most clean diesels, the Cruze uses a common rail piezo injection system. That means high pressure and a need for common sense when servicing.
According to Mike Siegrist, chief engineer on the project, there were four main areas the engineering team focused on; emissions, diagnostics, environmental conditions (of the U.S. market) and altitude. Siegrist noted in his AutoblogGreen interview that America has higher altitudes to deal with than Europe does and stricter emissions regulations to meet, all of which necessitated the engineering improvements before GM could bring the 2.0 to the States.
Like most of today’s low emissions diesels, the 2.0 is turbocharged and uses a common rail injection system with piezo injection. The U.S. versions gets a new aluminum intake manifold and throttle body, a larger capacity Exhaust Gas Recirculation (EGR) cooler, ceramic glow plugs and an engine oil heater. With the updates, the emissions of the U.S. version are significantly cleaner than the European original. The concession is a slight loss of power, though, with an estimated 148 hp output versus the Euro’s 163. You’ll likely not miss the extra ponies, as the U.S. version is equipped with an “overboost” feature capable of increasing torque from its rated 250 foot-pounds to 280 foot-pounds when needed. Not bad for an engine expected to deliver 46 mpg highway and making it the most fuel efficient non-hybrid on the market today.
A Garrett turbo mounted close to the exhaust promotes efficiency.
Tech Features
The new intake is a big player in helping the Cruze deliver on its fuel economy promises. GM engineers refer to the design as a “variable swirl intake system.” According to Siegrist, the system is designed to increase the mixture motion of air and fuel in low-speed, low-load driving. Each cylinder has two intake ports, one of which is controlled by a mechanical valve. During the variable swirl process, each throttle valve varies its opening amount to improve the mixture motion of the incoming air/fuel charge. The valves are controlled by the Engine Control Module (ECM) to insure optimum performance.
Other than a big green fuel cap and a label on the fuel door, GM currently has no provisions to prevent fueling mistakes on the diesel model. Ultra Low Sulfur Highway diesel fuel is recommended (2-D) but the engine is approved for up to B20 biodiesel as well. In addition to specific fuel recommendations, the Cruze requires dexos 2™ engine oil. Keep in mind that some products may say they meet dexos specs, but if they aren’t specifically certified, don’t use it. You can find out what products are properly certified at www.gmdexos.com. The transmission, likewise, requires a specific fluid (AW-1) and GM is clear to state that the use of DEXRON™ VI is not approved.
In addition to the normal stock of fluids, you’ll need to consider keeping some diesel exhaust fluid (DEF) on hand if you don’t already. Most new diesel powertrains are using urea injection and particulate filters for NOx emissions reduction. The fill for the urea tank on the Cruze is in the trunk. Not a bad idea, as it helps to avoid accidental filling of the tank with coolant or windshield wiper fluid, a common (and costly) mistake when the fill is located under the hood. The tank capacity is 4.9 gallons, enough for about 10,000 miles of ordinary driving, and is designed to coincide with routine oil change intervals to make servicing easier on the owner.
The DEF tank is located in the trunk. Use caution when filling.
The DEF fluid level indicator is displayed in the Driver’s Information Center (DIC). When the tank is nearing empty, a warning message will be displayed. If the tank is not refilled, the ECM will start limiting vehicle speed starting at 65 mph. Over time, speed will continue to reduce to a limit of 10 mph. A fill of at least two gallons is required to release the limitation. DEF fluid is made up of a mixture of synthetic urea (32.5 percent) and deionized water (67.5 percent). It is considered corrosive and should be handled with care. Use skin and eye protection, don’t overfill the tank and don’t spill it on the car.
Urea injection is used in a process called Selective Catalyst Reduction (SCR). Diesel engines run at an over-stoichiometric air/fuel ratio to ensure the combustion of soot and prevent unburned fuel from passing through the exhaust. The excess oxygen, though, encourages the emissions of nitrogen oxides. Diesel exhaust fluid is precisely metered into the exhaust stream where it vaporizes and decomposes to form ammonia and carbon dioxide. This leads to a catalytic reaction with NOx to form water and nitrogen, resulting in near zero NOx levels leaving the tailpipe.
A Look Underneath
If all you’ve ever worked on is gasoline engines, taking a look at the Cruze’s exhaust line will leave you with a lot of questions. First, there are so many things sticking out of it. From the engine back, you’ll find an oxygen (lambda) sensor, upstream NOx sensor, exhaust gas temperature (EGT) sensors (before and after the oxidation catalyst), a diesel particulate filter (DPF) pressure sensor, yet another EGT sensor, the DEF fluid injector, a downstream NOx sensor and finally a particulate matter (PMS) sensor. That’s a lot of inputs on one exhaust, but it is all necessary as part of the exhaust aftertreatment system needed to meet stringent emissions standards.
Lots of things sticking out of the exhaust underneath. This is the DEF fluid injection module.
The first stop for the engine exhaust gasses is the Diesel Oxidation Catalyst (DOC). It functions similarly to the catalytic converters you’re familiar with and must reach operating temperature before it can do its job of converting hydrocarbons (HC) and carbon monoxide (CO) into water and CO2. The point at which the DOC reaches that temperature is called “light off.” Knowing when that happens is important to the ECM, since the DOC provides the exhaust temperature needed for SCR. The three EGT sensors in the exhaust system monitor the temperature so the ECM knows when light off occurs. Proper function of the DOC relies on the use of ultra low sulfur fuel as recommended by the manufacturer.
Next in line is the DPF. As it’s name implies, the DPF captures small particulates, otherwise known as soot, and prevents their release into the air. Particulate heavy gasses enter into a filter substrate consisting of thousands of porous cells. Half of these cells are open on the inlet side but capped off at the other end. The other half are closed on the inlet side but open on the back end. More than 90 percent of the particulates are strained from the gasses as they pass through the porous material.
The PMS sensor monitors the amount of soot that gets by so the ECM knows how efficiently the DPF is working. The DPS sensor is similar to Ford’s DPFE sensor, in that it measures the pressure differential between the inlet and outlet of the particulate filter. This is a measure of how full the filter is becoming. If left unmonitored, the increasing backpressure eventually would choke off the engine and result in drivability issues.
Located after the SCR catalyst is the Particulate Matter Sensor (left) and the downstream NOx sensor (right).
When the pressure variance measured by the sensor indicates excessive build up, the ECM initiates a regeneration of the filter (cleaning the filter by burning off the collected particulates). This typically will occur during normal driving without the driver ever knowing it’s happening. Normal regeneration usually occurs with the vehicle traveling over 30 mph and it can take 20 to 30 minutes of continuous operation to perform a full regeneration process. During that time, extra fuel is injected into the engine to raise the exhaust gas temperatures to a level sufficient to clean the substrate. Should the driver slow to an idle condition during the normal regeneration mode, he may notice a slightly elevated idle speed to prevent thermal shock to the DPF catalyst.
If the owner operates his Cruze primarily at low speeds, or for short hops, normal regenerations might not be able to take place. If that happens, the DIC will alert him to the need to continue operation or illuminate the Service Engine Soon light and operate under reduced power mode until a manual regeneration is performed. A manual regeneration can be commanded using an OE or OE-equivalent scan tool.
No spare in the car. Only this air pump equipped with a sealant additive.
Finally, the exhaust gas is injected with the DEF discussed earlier to remove any NOx remaining in the exhaust stream before exiting the tailpipe. Upstream and downstream NOx sensors monitor the system’s function and allow for adjustments to the amount of DEF injected.
Sprechen Sie Deutsch?
“The Cruze Clean Turbo Diesel fills an important role in Chevrolet’s diverse four-cylinder lineup, and is primed to win over diesel devotees and compact car buyers with its performance, torque and fuel economy, “says Chris Perry, Chevrolet vice president of marketing.
And it’s pretty obvious that Chevy is looking straight down the barrel at the VW Jetta TDI as its primary competitor. One can’t help but to hear the distinct “tick” of the high pressure injection while standing outside the car but attention to sound dampening makes the noise almost imperceptible in the car and while driving. Equipped with a 6-speed Aisin automatic and a broad torque curve, the car performs well but won’t give anyone whiplash even if aggressively pushed. And it comes standard with a host of features not found on a base model Jetta; OnStar, turn-by-turn navigation, leather-trimmed power front seats, rearview camera, blind spot monitoring and more.
For an American car, its German is pretty good.
Subscribe to Motor Age and receive articles like this every month…absolutely free. Click here
