Here at Motor Age we like to keep content on the cutting edge and as we planned for this month’s feature, well over a year ago, we were hopeful that diesel technology would be appearing across the Asian vehicle product lines, particularly in platforms such as the Toyota Tundra and Tacoma, as well as other vehicles who’s market segment has been screaming for a diesel powerplant in the U.S. for years. Fast forward to today and we have yet to see the Asian diesel vehicle materialize. The Nissan Titan XD is the only one currently in production and just one more, the Mazda CX-5, on the way. We’ll spend some time taking a closer look at them both, as we’ll discuss some of the reasons that the expected diesel flood has instead been a slow trickle.
Nissan
Leading the way in Asian market diesel offerings is the Nissan Titan XD Pickup with an optional lightweight Cummins 5.0-liter V-8 Turbo Diesel. This diesel engine comes in at 1.7 liters shy of its Ram truck counterpart, the 6.7, and is rated at 310 horsepower with 500-600 Lb.-Ft of torque, making this mid-size pickup capable of towing a maximum load of 12,314 pounds. This power plant is the one that made Toyota truck fans giddy as rumors suggested that a similar unit could wind up in a Tundra at some point.
The technology on this Cummins power plant includes a proprietary M2© two-stage turbo designed to work at both low and high engine speeds, a Bosch high-pressure, common rail (HPCR) injection system and two-stage filtration system to capture any contaminants larger than 4 microns, protecting the HPCR system. The 5.0 also sports maintenance-free advanced glow plugs for cold startability.
Emissions on the Cummins engine include Cummins M2© Two-Stage Turbocharger, cooled Exhaust Gas Recirculation (EGR) and Cummins Emission Solutions After treatment System, which includes a Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR). According to Cummins this results “in near-zero oxides of nitrogen (NOx) and particulate matter (PM) emissions while delivering better performance and fuel economy.”
Overall this diesel power plant seems to get the job done but is unfortunately paired with the worst-selling pickup truck on the market. Give Nissan credit, however, they are at least trying to satiate the desires of the market segment that has been asking for an Asian diesel truck. Reviews of this truck since its inception have been fair to poor at best with complaints ranging from poor handling and fuel economy, excessive diesel exhaust fluid consumption due to a low capacity tank, and styling that is less than imaginative (some have called it an F-150 copy).
Mechanical issues including poor transmission performance as well as a variety of other issues uncovered by a simple Google search of “Nissan Diesel problems”. Poor pickup is also a complaint of the Cummins powered Titan. Interestingly, there were not many problems listed with the Cummins itself. Most of the complaints were typical of those we have seen as technicians over the course of working on the Nissan product line that have long made them a distant cousin to Toyota and Honda in terms of quality and reliability. Some other complaints are issues with failing radiators, door lock actuators and window motors.
While major issues on these Nissan trucks remain to be seen it is always a good idea to be prepared. The Nissan platform has one that has been known for needing reprogramming and as such a suitable J-2534 device is required. Some have also moved to the CONSULT-III, the factory tool for Nissan / Infiniti in order to ensure a cleaner programming transaction.
Mazda
The Mazda CX-5 Diesel is slated for sale in late 2017. The CX-5 will be the first diesel offering here in the states for Mazda and will feature Mazda Skyactiv-D technology. Mazda claims this engine to be “the world’s lowest compression ratio diesel” at 14:1 and boats this to be a clean, highly efficient engine that “will comply with strict exhaust gas regulations globally without the aid of expensive NOx (nitrogen oxides) aftertreatment systems.” According to Mazda, Features of the Skyactiv-D platform include “20 percent better fuel efficiency thanks to the low compression ratio of 14.0:1.” Mazda does not specify what the 20 percent is in comparison to which makes it difficult to judge what the rated fuel economy will actually be. Also featured, and similar to the Cummins offering, is a newly developed, two-stage turbo charger. This dual stage trend is also making its way into other brands such as Lexus (On the NX 2.0), but the Mazda will be the first proprietary two-stage on a diesel here in the US. Mazda claims this turbo will also lend itself to providing superior throttle response and torque in all RPM ranges. Emissions on the Skyactiv-D “Comply with global emissions regulations (Euro6 in Europe and the Post New Long-Term Regulations in Japan), without expensive NOx aftertreatment,” according to the automaker.
| (Images courtesy of Mazda Media) The Mazda CX-5 with Skyactiv-D diesel is slated for launch in late 2017. |
Mazda to-date has been light on actual specifications but they do provide some insight into the technology that will be a part of the Skyactiv-D package. The leading technological advancement is the use of the lowered compression ratio. As a Professor in an automotive program I have always taught my students that compression ratios in a diesel engine can range anywhere from 18:1 to 21:1 in typical applications. With such a high compression ratio diesel engines utilize the heat of compression to create a combustion event. According to Mazda, “If fuel is injected under these conditions, ignition will take place before an adequate air-fuel mixture is formed, causing heterogeneous combustion to occur locally. As a result, the formation of NOx and, due to combustion with insufficient oxygen, the formation of soot are brought about.” Due to current emissions standards, many manufacturers utilize a strategy in which the combustion event is delayed (later injection) however this decimates fuel economy. Enter lower combustion ratio: “When the compression ratio is lowered, compression temperature and pressure at TDC decrease. Consequently, ignition takes longer even when fuel is injected near TDC, enabling better mixture of air and fuel. This alleviates the formation of NOx and soot because the combustion becomes more uniform without localized high-temperature areas and oxygen insufficiencies. Furthermore, injection and combustion close to TDC result in a highly-efficient diesel engine, in which a larger amount of actual work (or, a higher expansion ratio) is obtained than in a high-compression-ratio diesel engine.”
Another impressive accomplishment by Mazda is the ability to lighten the diesel engine package. By running a lower compression ratio, Mazda was able to use less robust engine internals. “For example, it became possible to change the cylinder block's material to aluminum, which saved 25kg (vs. current diesel). The cylinder head became 3kg lighter with thinner walls and an integrated exhaust manifold. As for the reciprocating parts, the weight of the pistons were reduced by 25 percent. The crankshaft had its main journal diameter reduced from 60mm to 52mm, achieving a 25 percent weight reduction. As a result, the mechanical friction was greatly reduced to the same level as an average gasoline engine.”
Two main problems face automakers as they attempt to follow the Mazda CX-5 in regards to lower combustion ratio diesels. The first is cold startability and the second, misfiring. Mazda is dealing with the first by using a piezo injector that is capable of nine injection events per combustion cycle. These events will happen in three main categories: pre-injection, main injection and post-injection. Mazda states it will use various injection patterns dependent on driving condition and claims “definite engine start even with a low compression ratio is attributable to this precise injection control and also the adoption of ceramic glow plugs.” In order to deal with the issue of misfires after cold start, Mazda has developed a variable valve lift system (VVL) for the exhaust valves that will allow for the delay of the exhaust valve closing, keeping it partially open at the beginning of the intake stroke in order to keep much needed heat in the cylinder. The result of this is a more efficient combustion temperature that eliminates the misfire and smooths the idle.
Cold feet
In 2012, Arvind Thiruvengadam, an Assistant Professor at West Virginia University won a grant to research emissions output on diesel vehicles. Thiruvengadam’s lab was a modest, smallish space but his results would have a profound impact. Let’s call him the David of our story.
As the story goes, David would come up against a giant named Goliath, or Volkswagen, if you would rather. It turns out that during the course of his research, our David discovered that Volkswagen’s diesel vehicles were not performing the way that Volkswagen had claimed in terms of their emissions. The lab at WVU tested BMW diesels without uncovering a problem but after repeated tests of the Volkswagen deduced that something was amiss. WVU called the Environmental Protection Agency and the California Air Research Board (CARB) and told them what they had found. In order to get through emissions testing a unique software program had to be designed and installed that would allow the vehicle to run within emissions standards while being tested, yet perform differently when under normal driving conditions. This type of scheme took thought and planning. This scheme has cost Volkswagen over $18 billion and has resulted in a stock plunge from 253 Euro’s to just 92 Euro’s in a period of six months. As of June 1, 2017 the stock price was just 135 Euro’s, a shadow of where Volkswagen, at one point the world’s leading brand, once was.
On May 23, 2017, The U.S. Justice Department filed a lawsuit against Fiat Chrysler Automobiles for allegedly building and selling diesel engine vehicles that violated pollution standards. FCA immediately responded that they had not intentionally tried to cheat emissions standards and would fight the allegation.
Put these stories together and you have a recipe for a U.S. Asian diesel market that has failure to launch. While Mazda and Nissan are sticking their necks out it is hard to imagine that Asian vehicle icons such as Toyota and Honda will follow. Nissan and Mazda need to be proactive in order to continue to fight for market share but Honda and Toyota simply don’t need to sell a diesel in the U.S. It really is that simple. It remains to be seen what the future will hold but for now the Asian vehicle manufacturers have cold feet. There is simply too much to risk to go down the same road that Volkswagen and potentially others have in order to meet a relatively small market segment demand.
